Method for manufacturing optical film laminate including polarizing film

ABSTRACT

A method for manufacturing an optical film laminate including subjecting a laminate including the non-crystallizable ester type thermoplastic resin substrate and the polyvinyl alcohol type resin layer formed on the non-crystallizable ester type thermoplastic resin substrate to an elevated temperature in-air stretching to form a stretched laminate comprising a stretched intermediate consisting of a molecularly oriented polyvinyl alcohol type resin, impregnating the dichroic material in the stretched laminate to form a dyed laminate including a dyed intermediate comprising a polyvinyl alcohol type resin layer having the dichroic material impregnated therein in an oriented state, and stretching the dyed laminate in boric acid solution to form an optical film laminate.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims the priority of Japanese Patent Application No.2010-197413 filed on Sep. 3, 2010, and Japanese Patent Application No.2010-263692 filed on Nov. 26, 2010 in the JPO (Japan Patent Office), thedisclosure of which is incorporated herein in their entirety byreference.

TECHNICAL FIELD

The present invention relates to a method for manufacturing an opticalfilm laminate including a polarizing film. The polarizing filmmanufactured according to the present invention is a polarizing filmcomprising a polyvinyl alcohol type resin having a dichroic materialimpregnated therein in an oriented state and formed on anon-crystallizable ester type thermoplastic resin substrate.

BACKGROUND ART

A well-known method for manufacturing a polarizing film or a so-calledpolarizer (hereinafter, referred as “a polarizing film”) comprises stepsof subjecting a film of polyvinyl alcohol resin type material(hereinafter, referred as “PVA type resin”) to dyeing and stretchingprocesses to thereby provide a stretched film having a dichroic materialimpregnated therein with an oriented state. Among them, a polarizingfilm manufactured using a thermoplastic resin substrate and a method ofmanufacturing the same have been already known publicly as shown in theconceptual diagram of the FIG. 24.

As specific examples, reference test samples 1 and 3 are referred to. Inthe case of the reference test sample 1, a solution of PVA type resin iscoated on a thermoplastic resin substrate and then dried to form alaminate having a thin PVA type resin layer formed on the thermoplasticresin substrate. The formed laminate is stretched in air at a stretchingtemperature of 110° C. using, for example, a stretching device arrangedin an oven. Then, the PVA type resin layer having an oriented molecularstructure created by the stretching is subjected to a dyeing process tohave it impregnated with a dichroic material. Alternatively, in the caseof the reference test sample 3, the formed laminate is first subjectedto dyeing process to have the dichroic material impregnated therein.Then, the laminate having the dichroic material impregnated therein isstretched in air at a stretching temperature of 90° C. Such polarizingfilm comprising a PVA type resin including a dichroic material in anoriented state has been already publicly known as disclosed in thePatent Documents 2 to 5.

The method for manufacturing a polarizing film using a thermoplasticresin substrate is noticeable in that it allowed for uniformlymanufacturing the polarizing film compared with the method formanufacturing a polarizing film with a mono-layer of the PVA type resin.In the case of a polarizing film which is to be adhesively attached toeach of the opposite surfaces of a liquid-crystal cell for use in aliquid-crystal display apparatus, according to the method formanufacturing a polarizing film with a mono-layer of the PVA type resinas disclosed in Japanese Patent Application Publication JP2005-266325A(the Patent Document 1), the polarizing film is manufactured, forexample, by transporting a PVA type resin mono-layer of a thickness of50 to 80 μm through a transporting apparatus comprising a plurality setsof rolls driven at different peripheral speeds, and immersing the PVAtype resin mono-layer in a dyeing solution to have a dichroic materialimpregnated therein, while stretching the PVA type resin mono-layer inthe dichroic material solution at around 60° C. What is manufactured isa mono-layer polarizing film with a thickness of 15 to 35 μm. Presently,the polarizing film manufactured using the method has optical propertiesof a single layer transmittance of 42% or higher and a polarization rateof 99.95% or higher, and is used for a large-sized screen television.

However, since the PVA type resin is hydrophilic, a polarizing film issensitive to change of temperature and humidity and is apt to producechanges in dimensions such as expansion or shrinkage due to changes inenvironmental conditions possibly resulting in cracks. In order tosuppress expansion and shrinkage and to minimize effects of temperatureand/or humidity, it has been a usual practice in a polarizing film foruse with a television to provide a film of triacetylcellulose (TAC)having a thickness of 40 to 80 μm laminated on each of the oppositesurfaces of the polarizing film as a protection film. It should howeverbe noted that, in the case of a mono-layer polarizing film, since thereis a certain limit in reducing the thickness of the polarizing film, itis still difficult to completely restrict the expansion or shrinkage, sothat, when an optical film laminate including such polarizing film isadhesively attached to a component such as an adjacent optical film or aliquid-crystal cell through a layer of a bonding or adhesive agent, astress is induced in such component by the expansion or shrinkage of thepolarizing film. Such stress may cause a distortion in the displayedimage in a liquid-crystal display apparatus. Since the image distortionis caused by an optical elasticity or deformation of the componentinduced by a stress produced under the shrinkage in the polarizing film,the material to be used for such component must be limited to be of alow optical elasticity and of low birefringent property in order toreduce the image distortion. In addition, since the stress producedunder the shrinkage of the polarizing film may possibly cause theoptical film laminate to be detached from the liquid-crystal cell, it isrequired to use an adhesive agent of a higher adhesive power. However,using such adhesive agent of high adhesive power makes re-workingoperation difficult. The above is the technical problem inherent to ause of a mono-layer polarizing film.

Under such circumstances, there is a need for a manufacture ofpolarizing films, which can be used in place of the method using amono-layer polarizing film in which difficulties have been encounteredin an effort for producing polarizing films of a decreased thickness.However, if a PVA type resin mono-layer film having a thickness smallerthan 50 μm is passed through a transporting apparatus including aplurality sets of rolls driven at different peripheral speeds andstretched in a dye solution around a temperature of 60° C. to produce apolarizing film having a thickness of 10 μm or less, the PVA type resinmono-layer comprised of a hydrophilic polymer composition may be atleast partially dissolved in the solution as the thickness is decreasedby stretching, or may be broken because of being unable to withstand thestretching stress. As such, it is difficult to stably manufacture apolarizing film from a PVA type resin mono-layer. Because of suchproblems, the methods disclosed in the Patent Documents 2 to 5 have beendeveloped as new manufacturing methods of polarizing films. In thosemethods, a polarizing film is manufactured by forming a layer of a PVAtype resin on a thermoplastic resin substrate of a certain thickness andstretching thus formed PVA type resin layer together with thethermoplastic resin substrate.

In the above method, a laminate comprising a thermoplastic resinsubstrate and a PVA type resin layer is stretched in air typically at astretching temperature of 60 to 110° C. using, for example, a stretchingapparatus arranged in an oven. Then, the PVA type resin layer havingmolecular orientation produced through the stretching is subjected to adyeing process to have a dichroic material impregnated therein.Alternatively, the PVA type resin layer in the laminate comprising thethermoplastic resin substrate and the PVA type resin layer is first dyedto have a dichroic material impregnated therein. Then, the laminatecomprising the PVA type resin layer having the dichroic materialimpregnated therein is stretched in air typically at a stretchingtemperature of 60 to 110° C. The above process is the method ofmanufacturing the polarizing film having the dichroic material in anoriented state as disclosed in the Patent Documents 2 to 5.

More particularly, a solution containing a PVA type resin is initiallyapplied onto a thermoplastic resin substrate, and moisture content isremoved by a drying process to form a PVA type resin layer with athickness of several tens micrometer. Then, a laminate comprising thethermoplastic resin substrate and the PVA type resin layer is stretchedin air under an elevated temperature provided by a stretching apparatusarranged in an oven. The stretched laminate is then immersed in a dyeingsolution to have a dichroic material impregnated in the PVA type resinlayer, to form a polarizing film of a few micrometer thick having thedichroic material in an oriented state. The above is a conventionalmanufacturing method of a polarizing film using a thermoplastic resinsubstrate.

The polarizing film produced by the aforementioned manufacturing processis promising from viewpoint of reducing the thickness of a large sizedisplay element, eliminating distortions in displayed images andreducing industrial waste. However, up to now, it has been experiencedthat the polarizing film manufactured by the aforementioned process hasa lower degree of optical properties in terms of the polarizingperformance, as shown in FIG. 26 illustrating the optical properties ofthe reference test samples 1 to 3, and thus, there is still unsolvedtechnical problem in an effort for producing a thin polarizing film witha sufficiently high optical property.

The prior art documents referred to in the above and followingdescriptions are listed below.

-   Patent Document 1: Japanese Laid-Open Patent Publication    JP2005-266325A-   Patent Document 2: Japanese Patent 4279944B-   Patent Document 3: Japanese Laid-Open Patent Publication    JP2001-343521A-   Patent Document 4: Japanese Patent Publication JP8-12296B-   Patent Document 5: U.S. Pat. No. 4,659,523-   Non-Patent Document 1: H. W. Siesler, Advanced Polymeric Science,    65, 1, 1984

DISCLOSURE OF THE INVENTION Problem to be Solved by the Invention

The process of steadily manufacturing polarizing film using athermoplastic resin substrate has been discussed with reference to thePatent Documents 2 to 5. It should however be noted that in thesemethods, it has not as yet been possible to obtain polarizing filmsmeeting requirements for optical properties of contrast ratio of 1000:1or more and maximum luminance of 500 cd/m² or more which are requiredfor display elements of liquid-crystal display televisions.

This technical problem is simple and because of such simplicity it isnot easy to solve as will be described in the followings. According toanyone of the conventional manufacturing methods, stretching of alaminate comprising a thermoplastic resin substrate and a PVA type resinlayer formed thereon has been carried out in an environment ofhigh-temperature air. A primary reason for such stretching in air undera high temperature environment is that the thermoplastic resin substrateand the PVA type resin layer cannot be stretched at a temperature belowrespective glass transition temperatures (Tg). The Tg of PVA type resinis 75 to 80° C. The Tg of polyethylene terephthalate (PET) which is anester type thermoplastic resin is 80° C. For reference, the Tg ofnon-crystallizable PET having isophthalic acid copolymerized PET is 75°C. Thus, a laminate comprising a thermoplastic resin substrate and a PVAtype resin layer has to be stretched under an elevated temperaturehigher than those glass transition temperatures. As a matter of fact,the molecular orientation of a PVA type resin is enhanced by stretching.Polarizing performance of a polarizing film comprising a PVA type resindepends on the molecular orientation of the PVA type resin having adichroic material such as iodine impregnated therein. The polarizingperformance of the polarizing film comprising the PVA type resin isimproved with increase in the molecular orientation of the PVA typeresin.

However, a crystallizable resin, regardless whether it is an olefin oran ester, has generally a tendency of its molecules being oriented withan increase in temperature and with a stretching, resulting in anenhanced crystallization. Such crystallization causes various changes inphysical properties of a resin. A typical example is that the resinactually becomes unstretchable due to crystallization. In the case of acrystallizable resin, even in the case of an amorphous PET,crystallization rate abruptly increases at 120° C. and it becomesunstretchable at 130° C. As described later with reference to generalmaterial properties of thermoplastic resins, it has been known toprovide measures for suppressing crystallization by inhibiting polymermolecular orientation caused by heating or stretching. It is needless tomention that non-crystallizable olefin type resin and non-crystallizableester type resin produced with such process have also been well-known.For example, a unit which may inhibit crystallization of PET may becopolymerized with PET to form a non-crystallizable PET in whichcrystallization is suppressed. The crystallization rate does notabruptly increases at around 120° C. in the case of a non-crystallizablePET. Although crystallization of the non-crystallizable PET maygradually progress, it may be possible to stretch steadily under atemperature as high as 170° C. The non-crystallizable PET becomesunstretchable at a temperature higher than 170° C. due to softening ofthe PET.

The present invention aims at providing a method for manufacturing anoptical film laminate including a polarizing film having superioroptical properties of a reduced thickness compared with a conventionalpolarizing film.

Means for Solving the Problem

The inventors of the present invention have made extensive efforts inobtaining a polarizing film of a reduced thickness and improving opticalproperties of such polarizing film of a reduced thickness. As theresults, the inventors have been successful in obtaining a polarizingfilm comprising a PVA type resin in which a dichroic material isimpregnated therein, and a method for manufacturing the same. A thinpolarizing film can be produced by stretching a non-crystallizable estertype thermoplastic resin substrate together with a PVA type resin layerformed thereon.

According to researches and analysis by the inventors, it is notpossible to find any case where a non-crystallizable PET is used as athermoplastic resin substrate, and a laminate comprising a PVA typeresin layer formed on the non-crystallizable PET substrate is stretchedin end-free uniaxial stretching at a stretching temperature of 120° C.or higher and a stretching ratio of 5.0 or more. The present inventorshave challenged the above process to realize the present invention.

Each of FIGS. 18 to 22 is a schematic diagram based on experimentalresults. FIG. 18 is a schematic diagram, based on an experiment, showinga relationship between a stretching temperature and a stretchable ratiofor each of a crystallizable PET, a non-crystallizable PET and a PVAtype resin.

The thick solid line in FIG. 18 shows a relationship between thepractically realizable stretching ratio of a non-crystallizable PET andthe stretching temperature. The Tg of the non-crystallizable PET is 75°C. in this instance and it cannot be stretched at a temperature belowthe Tg. The stretching ratio of the non-crystallizable PET may be 7.0 ormore at a stretching temperature of 110° C. or higher in end-freeuniaxial elevated temperature in-air stretching. The thin solid line inFIG. 18 shows a relationship between the practically realizablestretching ratio of a crystallizable PET and the stretching temperature.The Tg of the crystallizable PET in this instance is 80° C. and itcannot be stretched at a temperature below the Tg.

FIG. 19 is a schematic diagram showing a change of the crystallizationrate of each of crystallizable PET and a non-crystallizable PET with achange of stretching temperature between the Tg and melting point (Tm)of the PET. It is understood from FIG. 19 that the crystallizable PET inamorphous state at 80 to 110° C. rapidly crystallizes at around 120° C.

As is clear from FIG. 18, a stretchable ratio of the crystallizable PETin end-free uniaxial elevated temperature in-air stretching is limitedto 4.5 to 5.5, and an applicable stretching temperature is in a verylimited range of 90 to 110° C.

Reference test samples 1 to 3 are examples of products obtained by theend-free uniaxial elevated temperature in-air stretching. Each of thereference test samples 1 to 3 comprises a polarizing film with athickness of 3.3 μm, formed by the end-free uniaxial elevatedtemperature in-air stretching of a laminate comprising a 7 μm-thick PVAlayer formed on a 200 μm-thick crystallizable PET substrate. Stretchingtemperature of each of the reference test samples is different such thatthe reference test sample 1 is 110° C., the reference test sample 2 is100° C. and the reference test sample 3 is 90° C. It should be notedthat the limit of stretchable ratio of the reference test sample 1 is4.0, and those for the reference test samples 2 and 3 are both 4.5.Stretching beyond those stretchable ratios was not possible because thelaminate itself was finally broken. It should however be noted that, inthe above results, it is not possible to deny that the restriction haspartly been influenced by the stretchable ratio of the PVA type resinlayer formed on the crystallizable PET.

Reference is now made to the broken line in FIG. 18. This diagram showsa realizable stretching ratio of a PVA which belongs to PVA type resins.The Tg of a PVA type resin is 75 to 80° C. and a mono-layer of a PVAcannot be stretched at a temperature below the Tg. As is clear from FIG.18, the realizable stretching ratio of the mono-layer of a PVA in theend-free uniaxial elevated temperature in-air stretching is limited to5.0. Thus, the present inventors have arrived at a conclusion that, fromthe relationship between the stretching temperature and the realizablestretching ratio of each of a crystallizable PET and a PVA, therealizable stretching ratio under the end-free uniaxial elevatedtemperature in-air stretching of the laminate comprising the PVA typeresin layer formed on the crystallizable PET is limited to 4.0 to 5.0 ata stretching temperature in the range of 90 to 110° C.

Comparative test samples 1 and 2 are examples of the end-free uniaxialelevated temperature in-air stretching of a laminate comprising a PVAtype resin layer formed on a non-crystallizable PET substrate.Stretching temperature does not restrict stretching of thenon-crystallizable PET substrate. The comparative test sample 1 is apolarizing film formed by the end-free uniaxial elevated temperaturein-air stretching of a laminate comprising a 7 μm-thick PVA layer formedon a 200 μm-thick non-crystallizable PET substrate at a stretchingtemperature of 130° C. with a stretching ratio of 4.0.

Reference is made to the Comparative Table in Table 1. The comparativetest samples 2 include those cases wherein polarizing films, similar tothe comparative test sample 1, are formed by an end-free uniaxialelevated temperature in-air stretching of a laminate comprising a 7μm-thick PVA layer formed on a 200 μm-thick non-crystallizable PETsubstrate under different stretching ratio of 4.5, 5.0 and 6.0. As shownin Table 1, in each case of the comparative test samples, there havebeen non-uniform stretching or breakage produced in film surface of thePET substrate, and a breakage in the PVA type resin layer at astretching ratio of 4.5. It has been confirmed with the results that thestretching ratio under the end-free uniaxial elevated temperature in-airstretching at a stretching temperature of 130° C. is limited to be 4.0.

TABLE 1 Comparative Table Stretched film Non-crystallizable Laminate ofPVA PET substrate type resin layer (isophthalic acid and StretchingStretching copolymerized non-crystallizable temp. ratio PET) PETsubstrate Comp. 130° C. 4.0 Uniformly Uniformly test stretched withoutstretched without sample 1 breaking breaking Comp. 4.5 Not uniformly PVAtype resin test stretched without layer and samples 2 breakingnon-crystallizable PET substrate both broken 5.0 Not uniformly Notinvestigated stretched without breaking 6.0 Broken Not investigated

In respective ones of the reference test samples 1 to 3, althoughstretching temperature is different, a dyed laminate has been producedwith a laminate comprising a PVA type resin layer formed on acrystallizable PET substrate by stretching the laminate at a stretchingratio of 4.0 to 4.5 to have a PVA type resin layer with oriented PVAmolecules and iodine impregnated therein. Specifically, the stretchedlaminate was immersed in a dyeing solution containing iodine andpotassium iodide at a temperature of 30° C. for an appropriate timeperiod to have iodine impregnated in the PVA type resin layer in thestretched laminate, such that the single layer transmittance of the PVAtype resin layer finally constituting the polarizing film becomes 40 to44%. In addition, by adjusting the amount of iodine impregnated in thethin PVA type resin layer, various polarizing films have been producedwith different single layer transmittance T and polarization rate P.

Reference is now made to the diagram in FIG. 25. FIG. 25 shows opticalproperties of the reference test samples 1 to 3. PVA molecules in thePVA type resin layer formed on the crystallizable PET substrate areoriented to a certain degree by the elevated temperature in-airstretching. On the other hand, it is presumed that the in-air stretchingunder such elevated temperature may facilitate crystallization of thePVA molecules preventing orientation of non-crystallized portion ofmolecules.

In view of such observations, the present inventors have developed,prior to the present invention, a polarizing film shown in thecomparative test sample 3 and the method for manufacturing the same. Thedevelopment is based on a surprising finding of plasticizing function ofwater wherein a laminate comprising a PVA type resin layer formed on aPET substrate can be stretched even under a stretching temperature belowthe Tg. According to the method, it was confirmed that a laminatecomprising a PVA type resin layer formed on a PET substrate might bestretched to a stretching ratio of 5.0. This is the one corresponding tothe Example 1 disclosed in the assignee's application PCT/JP2010/001460.

The present inventors have conducted further research and realized thatthe stretching ratio has been limited to 5.0 due to a crystallizablenature of the PET used for a PET substrate. The inventors have initiallythought that the crystallizing property of the PET substrate such ascrystallizable or non-crystallizable would not significantly affectstretching operation because a laminate comprising a PVA type resinlayer formed on a PET substrate was stretched in boric acid solution ata temperature below the Tg, however, it was subsequently found that useof a non-crystallizable PET made it possible to stretch the laminate upto a stretching ratio of 5.5. Thus, it is presumed that the stretchingratio is limited in the manufacturing method of the polarizing filmshown in the comparative test sample 3 to a value of 5.5 due to thelimit in the non-crystallizable PET substrate.

For the comparative test sample 1, various polarizing films were formedwith different single layer transmittance T and polarization rate P, theoptical properties thereof being shown in FIG. 25 together with thereference test samples 1 to 3.

Reference is now made to FIG. 20 which is a diagram simply showing therelationship between the stretching ratio obtained by an elevatedtemperature in-air stretching, and a total stretching ratio (hereinafterreferred as “a total stretching ratio”) obtained by a two stagestretching including the elevated temperature in-air stretching and asecond stretching in accordance with the present invention which hasbeen created based on the research results of the present inventors. Thehorizontal axis of the diagram designates the stretching ratio under theend-free uniaxial elevated temperature in-air stretching at a stretchingtemperature of 130° C. The vertical axis of the diagram designates thetotal stretching ratio obtained by a two stage stretching including theend-free uniaxial elevated temperature in-air stretching, the totalstretching ratio having been calculated based on the original lengthbefore the elevated temperature in-air stretching which has been takenas one and equivalent to the ratio of magnification of the final lengthwith respect to the original length. For example, in the case where thestretching ratio under the end-free uniaxial elevated temperature in-airstretching at a stretching temperature of 130° C. is 2.0 and stretchingratio under the second stage stretching is 3.0, the resultant totalstretching ratio will be 2.0×3.0=6.0. The second stage stretching afterthe elevated temperature in-air stretching may be carried out as anend-free uniaxial stretching in boric acid solution at a stretchingtemperature of 65° C. (stretching a laminate immersed in a boric acidsolution is hereinafter referred as “in-boric-acid-solutionstretching”). The inventors have obtained the result as shown in FIG. 20by a combination of the two stage stretching.

The solid line in FIG. 20 shows a stretching ratio attainable using anon-crystallizable PET. The total stretching ratio of thenon-crystallizable PET is limited to 5.5 with the elevated temperaturein-air stretching ratio of 1.0, i.e. when the non-crystallizable PET isdirectly stretched by the in-boric acid solution stretching without theelevated temperature in-air stretching. It indicates that thenon-crystallizable PET will break if stretched beyond this value, butthe ratio is merely the minimum stretching ratio of thenon-crystallizable PET, and the diagram shows that the larger thestretching ratio of elevated temperature in-air stretching, the largerthe total stretching ratio of the non-crystallizable PET, and thestretchable ratio may be beyond 10.0.

On the other hand, the broken line in FIG. 20 shows the stretching ratioattainable in a PVA non-crystallizable. The total stretching ratio ofthe PVA is at the maximum 7.0 when the PVA is directly stretched by thein-boric-acid-solution stretching without the elevated temperaturein-air stretching. However, the larger the stretching ratio of elevatedtemperature in-air stretching, the smaller the total stretching ratio ofthe PVA, and the total stretching ratio of the PVA may fall below 6.0when the elevated temperature in-air stretching ratio is 3.0. The PVAwill break if it is attempted to increase the total stretching ratio ofthe PVA up to 6.0. As will be understood from FIG. 20, the reason forthe laminate comprising a PVA type resin layer formed on anon-crystallizable PET substrate becoming impossible to be stretchedchanges depending on the amount of the stretching ratio under theelevated temperature in-air stretching, from that induced by thenon-crystallizable PET substrate to that induced by the PVA type resinlayer. For reference, the stretching ratio of PVA under the in-airstretching is up to 4.0, and the PVA cannot be stretched beyond thisvalue. It is assumed that this stretching ratio corresponds to the totalstretching ratio of the PVA.

Reference is now made to the diagram in FIG. 21. FIG. 21 is a schematicdiagram showing the relationship between the stretching temperature inthe elevated temperature in-air stretching and the total stretchingratio obtainable by carrying out both the elevated temperature in-airstretching and the in-boric acid solution stretching, for anon-crystallizable PET and a PVA type resin, the relationship beingdetermined based on experiments. In FIG. 18, the diagram shows thestretching temperature for the elevated temperature in-air stretching onthe horizontal axis, and the attainable stretching ratio with theelevated temperature in-air stretching on the vertical axis, for thenon-crystallizable PET and the PVA type resin. FIG. 21 is different fromFIG. 18 in that the horizontal axis is the stretching temperature whenthe elevated temperature in-air stretching ratio is 2.0, and thevertical axis is the total stretching ratio attainable with the elevatedtemperature in-air stretching and the in-boric-acid-solution stretching.

As will be described later, the present invention has been created bycombining 2 stretching processes, the elevated temperature in-airstretching and the in-boric acid solution stretching, which is notmerely a combination of 2 stretching processes, but it is to be notedthat the invention could be accomplished based on the surprisingfindings that the following two technical problems could besimultaneously solved by the combination. There exist two technicalproblems that have conventionally been considered impossible to solve.

The first technical problem is that the stretching ratio and thestretching temperature which are governing factors for improvingorientation of a PVA type resin are largely restricted by thethermoplastic resin substrate having a PVA type resin layer formedthereon.

The second technical problem is that, even if the restriction for thestretching ratio and the stretching temperature are cleared,crystallization and stretchability of a crystallizable resin such as aPVA and a PET are physical properties which are not compatible with eachother, so that the amount of stretching of the PVA can be restricted byits crystallization.

The first technical problem will further be discussed in the followings.In manufacturing a polarizing film using a thermoplastic resinsubstrate, there is a restriction induced by the properties of the PVAin that the stretching temperature should be above the Tg of the PVA (75to 80° C.) and the stretching ratio should be 4.5 to 5.0. If acrystallizable PET is used as the thermoplastic resin substrate, thestretching temperature is further restricted to 90 to 110° C. It hasbeen considered that a polarizing film, produced through the elevatedtemperature in-air stretching of the aforementioned type laminate forthinning down the PVA type resin layer formed on a thermoplastic resinsubstrate included in the laminate, cannot be free from suchrestriction.

To address this, the present inventors has previously proposed anin-boric-acid-solution stretching process that can take place of theelevated temperature in-air stretching, and that is based on finding ofa plasticizing function of water. It should however be noted that, evenwith the in-boric acid solution stretching at a stretching temperatureof 60 to 85° C., it has been difficult to overcome the restrictionsinduced by the thermoplastic resin substrate where the stretching ratiousing a crystallizable PET is limited at 5.0 and the stretching ratiousing a non-crystallizable PET is limited at 5.5. Thus, the firsttechnical problem is that, improvement of orientation of PVA moleculesis restricted as above which in turn restricts optical properties of athin polarizing film.

The solution to the first technical problem can be explained withreference to schematic diagrams shown in FIG. 22. There are shown twodiagrams in FIG. 22, wherein one shows molecular orientation of the PETconstituting the thermoplastic resin substrate and the other shows adegree of crystallization of the PET. The horizontal axis in each of thediagrams represents a total stretching ratio of elevated temperaturein-air stretching and in-boric-acid-solution stretching. The brokenlines in FIG. 22 show the total stretching ratio which can be attainedthrough the in-boric acid solution stretching alone. The extent ofcrystallization of the PET, regardless whether it is crystallizable ornon-crystallizable, abruptly increases at the total stretching ratiobetween 4.0 and 5.0. Thus, the stretching ratio of the in-boric acidsolution stretching was limited to 5.0 or 5.5. Whereat this point, themolecular orientation reaches the upper limit and the required tensionfor the stretching abruptly increases. In other words, it is impossibleto stretch beyond this point.

The solid lines in FIG. 22 show the results of the two stage stretchingwherein PET is subjected to a stretching in an end-free uniaxialelevated temperature in-air stretching to attain a stretching ratio of2.0 and at a stretching temperature of 110° C., then a furtherstretching in an in-boric acid solution stretching at a stretchingtemperature of 65° C. Regardless of whether the PET is crystallizable ornon-crystallizable, the extent of crystallization did not show anyabrupt increase, as opposed to the results obtained with only thein-boric acid solution stretching. As the result, the total stretchableratio has been improved up to 7.0 where the orientation reached theupper limit and the required tension for stretching has abruptlyincreased. As is clear from FIG. 21, this result owes to adopting theend-free uniaxial elevated temperature in-air stretching for the firststage stretching. When a end-fixed uniaxial elevated temperature in-airstretching is adopted as described later, the attainable totalstretching ratio can be increased to 8.5.

By solving the first technical problem, it has become possible toeliminate restrictions in the stretching ratio which has beenexperienced due to the property of the PET substrate, and to improvemolecular orientation of the PVA by increasing the total stretchingratio. Thus, the optical properties of the polarizing film can besignificantly improved. It should further be noted that the improvementof the optical properties had been more than those described above.Further improvements have been accomplished by solving the secondtechnical problem.

The second technical problem can be described as follows. One of thecharacteristic features of PVA and crystallizable resins such as a PETis that, in these resins, molecules tend to be oriented by heating andstretching resulting in a progress of crystallization. Stretching of aPVA is limited by crystallization of the resin that is crystallizable innature. Crystallization and stretchability are two opposing physicalproperties, and it has been considered that progress of crystallizationin a PVA tends to prevent its molecules from being orientated. This isthe second technical problem.

It is possible to describe a manner of solving the second technicalproblem with reference to FIG. 23. The solid line and the broken line inFIG. 23 show the relationship between the extent of crystallization andthe orientation function of a PVA calculated based on the results of twoexperiments.

The solid line in FIG. 23 shows the relationship between the extent ofcrystallization and the orientation function of the PVA in samplesprepared as follows. Six samples were prepared by forming laminatesprovided under the same condition, each laminate comprising a PVA typeresin layer formed on a non-crystallizable PET substrate. Stretchedlaminates each comprising a PVA type resin layer were produced bysubjecting thus prepared six laminates each comprising a PVA type layerto an elevated temperature in-air stretching at the same stretchingratio of 1.8, with different stretching temperatures of 80° C., 95° C.,110° C., 130° C., 150° C., and 170° C., respectively. Then, measurementshave been made on respective ones of the PVA type resin layers in thestretched laminates to determine and analyze the extent ofcrystallization and the orientation function. Details of the measuringand analyzing processes will be described later.

The broken line in FIG. 23 shows, as the solid line does, therelationship between the extent of crystallization and the orientationfunction of each of the PVA in samples prepared as follows. Six sampleswere prepared by forming laminates provided under the same condition,each laminate comprising a PVA type resin layer formed on anon-crystallizable PET substrate. Stretched laminates each comprising aPVA type resin layer were produced by subjecting thus prepared sixlaminates each comprising a PVA type layer to an elevated temperaturein-air stretching at the same stretching temperature of 130° C. withdifferent stretching ratio of 1.2, 1.5, 1.8, 2.2, 2.5, and 3.0,respectively. Then, measurements have been made on respective ones ofthe PVA type resin layers in the stretched laminates to determine andanalyze the extent of crystallization and the orientation function withprocesses which will be described later.

With the solid line in FIG. 23, it has been confirmed that the molecularorientation of the PVA is improved with increase of the stretchingtemperature in the elevated temperature in-air stretching of the PVAtype resin layer included in the stretched laminate. In addition, withthe broken line in FIG. 23, it has been confirmed that the molecularorientation of the PVA is improved with increase of the stretching ratiounder the elevated temperature in-air stretching of the PVA type resinlayer included in the stretched laminate. Improving the molecularorientation or enhancing the extent of crystallization of the PVA beforethe second stage in-boric acid solution stretching is effective toimprove the resulting molecular orientation of the PVA after thein-boric acid solution stretching. Further, it can be noticed in the T-Pdiagrams for the later described examples that, as the result of theimprovement of the molecular orientation of the PVA, it is also possibleto improve the molecular orientation of poly-iodide ion.

The inventors could obtain an unexpected, remarkable results that, byincreasing the stretching temperature or the stretching ratio during thefirst stage elevated temperature in-air stretching, the orientation ofPVA molecules in the PVA type resin layer produced after the secondstage in-boric acid solution stretching could be further enhanced.

It has been confirmed that the first technical problem can solved by thepreliminary or auxiliary stretching of the laminate comprising a PVAtype resin layer formed on the non-crystallizable PET substrate with thefirst stage elevated temperature in-air stretching, which allows forstretching the PVA type resin layer with a higher stretching ratio tothereby provide sufficient improvement of molecular orientation of PVAwithout encountering any restriction on the stretching ratio of anon-crystallizable PET substrate during the second stagein-boric-acid-solution stretching.

It is to be further noted that the solution to the second technicalproblem provided unexpected result that by adopting a higher stretchingtemperature for the preliminary or auxiliary stretching of the laminatecomprising the PVA type resin layer formed on the non-crystallizable PETsubstrate during the first stage elevated temperature in-air stretching,or by attaining a higher stretching ratio during the preliminary orauxiliary stretching, it is possible to attain a further improvement inthe orientation of the PVA molecules in the PVA type resin layer throughthe second stage in-boric-acid-solution stretching. In either of thecases, the first stage elevated temperature in-air stretching can beclassified as a preliminary or auxiliary in-air stretching with respectto the second stage in-boric-acid-solution stretching. Hereinafter, the“first stage elevated temperature in-air stretching” is referred as the“preliminary in-air stretching” with respect to the second stagein-boric-acid-solution stretching.

A mechanism for solving particularly the second technical problem byperforming the preliminary in-air stretching may be explained asfollows. As shown in FIG. 23, the molecular orientation in the PVA canbe enhanced by the preliminary in-air stretching with an increase in thestretching temperature or the stretching ratio during the preliminaryin-air stretching. It is assumed that the reason for this result is thatthe extent of crystallization of the PVA is enhanced with the increaseof the stretching temperature or the stretching ratio of the PVA, sothat the PVA is stretched while points of crosslink are being partiallyformed. As a result, the molecular orientation in the PVA is enhanced.It is assumed that by accomplishing such enhanced molecular orientationin the PVA with the preliminary in-air stretching prior to thein-boric-acid-solution stretching, it is possible to facilitatecross-linking of the boric acid with the PVA when the PVA is immersed inthe boric acid solution so that the PVA is stretched with the boric acidserving as junction points. As the result, the molecular orientation inthe PVA is enhanced even after the in-boric-acid-solution stretching.

The followings set forth modes of embodiments of the present invention.

The present invention relates to a method for manufacturing an opticalfilm laminate including a polarizing film comprising a polyvinyl alcoholtype resin formed on a non-crystallizable ester type thermoplastic resinsubstrate and having a dichroic material impregnated therein in anoriented state in the form of a continuous web, the method comprisingprocesses of:

subjecting a laminate comprising the non-crystallizable ester typethermoplastic resin substrate and the polyvinyl alcohol type resin layerformed on the non-crystallizable ester type thermoplastic resinsubstrate to a preliminary in-air stretching to form a stretchedlaminate comprising a stretched intermediate consisting of a molecularlyoriented polyvinyl alcohol type resin;

impregnating the dichroic material in the stretched laminate to form adyed laminate including a dyed intermediate comprising a polyvinylalcohol type resin layer having the dichroic material impregnatedtherein in an oriented state; and

stretching the dyed laminate in a boric acid solution to form an opticalfilm laminate including a polarizing film comprising the polyvinylalcohol type resin having the dichroic material impregnated therein inan oriented state.

The term “a preliminary in-air stretching” refers to, withoutlimitation, “a process of stretching a laminate in air at an elevatedtemperature” at a first stage using a heating device such as an oven. Inaddition, the term “in-boric-acid-solution stretching” refers to, forexample, without limitation, “a process of stretching a laminate whileimpregnating the laminate in boric acid solution” at a second stage.

In one aspect of the present invention, the method may include apolarizing film comprising polyvinyl alcohol type resin formed on anon-crystallizable ester type thermoplastic resin substrate in the formof a continuous web and having a dichroic material impregnated thereinin an oriented state, the polarizing film having optical property valuesin a range represented by the following formulae:P>−(10^(0.929T-42.4)−1)×100 (where T<42.3);andP≧99.9 (where T≧42.3)where: T represents a single layer transmittance T and P a polarizationrate.

In this regard, the range of the optical property values comprising thesingle layer transmittance T and the polarization rate P represented bythe above formulae is a performance required for a display for aliquid-crystal television using a large size display element.Specifically, the performance requirements are equivalent to a contrastratio of 1000:1 or higher, and, a maximum luminance of 500 cd/m² orhigher. Hereinafter, the performance requirements will simply bereferred as “required performance.” In addition, the polarizingperformance of either one of the polarizing films on a back light sideor a viewing side of liquid-crystal cells should meet at least the aboveconditions. If a polarizing film with the polarization rate (P) of 99.9%or less is used for either one of polarizing films attached to the backlight side or the viewing side, it will become impossible to attain thepolarizing performance as a whole in a liquid crystal display deviceeven if a polarizing film with the highest possible polarizingperformance is used for the other of the polarizing films.

In one aspect of the present invention, the may include a process offorming a PVA type resin layer on a non-crystallizable ester typethermoplastic resin substrate. This process may be considered as,without limitation, coating and drying the PVA type resin on thenon-crystallizable ester type thermoplastic resin substrate.

In one aspect of the present invention, it is preferable that thenon-crystallizable ester type thermoplastic resin substrate has athickness which is at least 6 times as large as that of the PVA typeresin layer as formed on the substrate, and more preferably at least 7times. By having the thickness of the non-crystallizable ester typethermoplastic resin substrate of at least 6 times as large as that ofthe PVA type resin layer, it is possible to suppress any possibleproblems such as breakage during transportation in manufacturing processinduced by insufficient film strength, and formation of curling ordeterioration of transferability when used as one of the polarizingfilms on a backlight side or a viewing side of a liquid-crystal display.

Reference is now made to FIG. 1. FIG. 1 shows a diagram which isprepared for the purpose of investigating if there may be any problemwhich may be caused by the relationship between the thickness of thenon-crystallizable ester type thermoplastic resin substrate and that ofthe coating (the thickness of the polarizing film) of the PVA type resinlayer. As shown in FIG. 1, with the ratio of the thicknesses of thenon-crystallizable ester type thermoplastic resin substrate to that ofthe PVA type resin layer of around 5.0, it is concerned that a problemmay arise during transportation

According to this aspect of the present invention, the thickness of thepolarizing film is preferably 10 μm or less. If the thickness of thepolarizing film is 3 to 10 μm or less, there are no significantdifferences among the polarizing performances of the polarizing filmswith thicknesses of 3 μm, 8 μm and 10 μm as shown in T-P graphs in FIG.2 which shows the polarizing performances of the polarizing film, and itis possible to confirm that the polarizing film has the opticalproperties which satisfy the above formulae. FIG. 2 shows that thepolarizing film which has a thickness of 10 μm or less obtains theoptical property satisfying the required performance without beingsubjected to the anti-crack property problem.

In one aspect of the invention, the non-crystallizable ester typethermoplastic resin substrate may be comprised of isophthalicacid-copolymerized polyethylene terephthalate,cyclohexanedimethanol-copolymerized polyethylene terephthalate, ornon-crystallizable polyethylene terephthalate comprising othercopolymerized polyethylene terephthalate. It is also preferable that thenon-crystallizable ester type thermoplastic resin substrate may becomprised of a transparent resin such that it serves as an opticallyfunctional film protecting a surface of the polarizing film. Inaddition, the dichroic material may be comprised of either iodine, or amixture of iodine and an organic dye.

In a further aspect of the invention, it is preferable that thepreliminary in-air stretching accomplishes a stretching ratio of 3.5 orless, and conducted under a stretching temperature higher than the glasstransition temperature of the PVA type resin. In addition, it ispreferable that the range of the stretching temperature of thepreliminary in-air stretching is 95° C. to 150° C.

In one aspect of the invention, a dyed laminate comprising a PVA typeresin layer having iodide impregnated therein in an oriented state maybe manufactured by, without limitation, immersing the stretched laminatecomprising the PVA type resin layer having an oriented molecularstructure created by the preliminary in-air stretching in a dyeingsolution comprised of the dichroic material such as iodide.

In a further aspect of the present invention, it is preferable topreliminary insolubilize the stretched laminate before immersing thelaminate in the dyeing solution. Specifically, without limitation, thisprocess includes a step of immersing the stretched intermediate for 30seconds in a boric acid solution under a solution temperature of 30° C.to insolubilize the PVA type resin layer included in the stretchedlaminate and having PVA molecules impregnated therein in an orientedstate. The boric acid insolubilizing solution used in this processcontains 3 parts in weight of boric acid with respect to 100 parts inweight of water. The technical problem to be solved by theinsolubilization process is to prevent the PVA type resin layer includedin the stretched laminate from dissolving at least in the dyeingprocess. This may be referred as the first insolubilization, and asecond insolubilization may be conducted as a process of insolubilizingthe dyed laminate including the PVA type resin layer having the dichroicmaterial impregnated therein in an oriented state by carrying out across-linking process by immersing the dyed laminate for 60 seconds inthe boric acid solution at a temperature of 40° C., before subjectingthe dyed laminate to the in-boric-acid-solution stretching. The firstand second insolubilization processes in this aspect of the presentinvention both have influences on the optical properties of the finallymanufactured polarizing films.

In one aspect of the present invention, when the preliminary in-airstretching is performed by an end-free uniaxial stretching, it ispreferable that the total stretching ratio of 5.0 or more and 7.5 orless is attained for the PVA type resin layer finally formed on thenon-crystallizable ester type thermoplastic resin substrate. Inaddition, when the preliminary in-air stretching is performed in anend-fixed uniaxial stretching, it is preferable that the totalstretching ratio of 5.0 or more and 8.5 or less is attained for the PVAtype resin layer finally formed on the non-crystallizable ester typethermoplastic resin substrate.

In one aspect of the present invention, the method may further include aprocess of cleaning the optical film laminate including the polarizingfilm comprising the PVA type resin having the dichroic materialimpregnated therein in the oriented state, with a solution containingiodide salt and having a temperature lower than the glass transitiontemperature of the non-crystallizable ester type thermoplastic resinsubstrate included in the optical film laminate. In addition, it ispossible that the method further includes a process of drying thecleaned optical film laminate at a temperature between 50° C. and 100°C.

In a further aspect of the present invention, the method may furtherinclude a process of attaching an optically functional film through abonding agent to a surface of the polarizing film opposite to thesurface which is attached to the non-crystallizable ester typethermoplastic resin substrate included in the dried optical filmlaminate. Alternatively, it is possible that the method further includesa process of attaching the optically functional film through the bondingagent to the surface of the polarizing film opposite to the surfacewhich is attached to the non-crystallizable ester type resin substrateincluded in the dried optical film laminate, and simultaneously peelingthe non-crystallizable ester type resin substrate from the polarizingfilm to transfer the polarizing film to the optically functional filmfor forming an optically functional film laminate which has thepolarizing film transferred to the optically functional film. There maybe a variety of structures in the manufactured optically functional filmlaminate as described in the followings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram showing an appropriate thickness of the resinsubstrate with respect to the thickness of the PVA type resin layer (orthe thickness of the polarizing film);

FIG. 2 is a comparative diagram of the polarizing performance of thepolarizing film with thicknesses of 3 μm, 8 μm and 10 μm;

FIG. 3 is a schematic diagram of T-P graphs showing the relationshipbetween the single layer transmittance and the polarization rate;

FIG. 4 is a diagram showing a range of required performance of thepolarizing film;

FIG. 5 is a diagram showing theoretical values of polarizing performancebased on the dichroic ratio of polarizing films 1 to 7;

FIG. 6 is a comparative table showing differences in dissolution of thePVA type resin layer in accordance with differences in iodineconcentration in dyeing bath;

FIG. 7 is a comparative diagram showing changes in the polarizingperformance of the polarizing film formed with the PVA type resin layerin accordance with changes in iodine concentration in dyeing bath;

FIG. 8 is a comparative diagram showing the polarizing performances ofthe polarizing films of examples 1 to 4.

FIG. 9 is a schematic drawing showing a manufacturing process forproducing an optical film laminate without insolubilization treatment;

FIG. 10 is a schematic drawing showing a manufacturing process forproducing an optical film laminate with insolubilization treatment;

FIG. 11 shows examples of optical film laminate wherein the polarizingfilm is laminated;

FIG. 12 shows examples of optically functional film laminate wherein thepolarizing film is laminated;

FIG. 13 is a comparative diagram showing the polarizing performance ofthe polarizing films (PVA layer thickness, non-crystallizable PETsubstrate) in accordance with the examples 4 to 6;

FIG. 14 is a comparative diagram showing the polarizing performance ofthe polarizing films (preliminary in-air stretching ratio) in accordancewith the examples 4 and 7 to 9;

FIG. 15 is a comparative diagram of polarizing performance of polarizingfilms (preliminary in-air stretching temperature) of examples 4, and 10to 12;

FIG. 16 is a comparative diagram of polarizing performance of polarizingfilms (total stretching ratio) of examples 4, and 13 to 15;

FIG. 17 is a diagram showing the polarizing performance of thepolarizing films produced by fixed-end uniaxial stretching process inaccordance with the examples 16 to 18;

FIG. 18 is a schematic diagram showing the relationship between thestretching temperature and the attainable stretching ratio of each ofthe crystallizable PET, the non-crystallizable PET and the PVA typeresin.

FIG. 19 is a schematic diagram showing changes in crystallization ratein accordance with temperature changes between Tg and Tm of thecrystallizable PET and the non-crystallizable PET;

FIG. 20 is a schematic diagram showing the relationship between thestretching ratio under the elevated temperature in-air stretching andthe total stretching ratio of the non-crystallizable PET and the PVAtype resin;

FIG. 21 is a schematic diagram showing the relationship between thestretching temperature in the elevated temperature in-air stretching andthe total attainable stretching ratio of each of the crystallizable PET,the non-crystallizable PET and the PVA type resin;

FIG. 22 is a schematic diagram showing the relationships between thetotal stretching ratio and the molecular orientation, and the extent ofcrystallization of the PET used as the thermoplastic resin substrate;

FIG. 23 is a diagram showing the relationship between the extent ofcrystallization and the orientation function of PVA;

FIG. 24 is a schematic drawing showing examples of manufacturing processof polarizing film using the thermoplastic resin substrate;

FIG. 25 is a diagram showing the polarizing performance of thepolarizing films in accordance with the comparative test sample 1 andthe reference test samples 1 to 3;

FIG. 26 is a list showing the manufacturing conditions of the polarizingfilms or the optical film laminates comprising the polarizing films inaccordance with the examples 1 to 10; and

FIG. 27 is a list showing the manufacturing conditions of the polarizingfilms or the optical film laminates comprising the polarizing films inaccordance with the examples 11 to 18.

BEST MODE FOR CARRYING OUT THE INVENTION

Descriptions will now be made on optical properties represented bymaterial properties of the thermoplastic resin substrate used in thepresent invention and the polarizing performance of the polarizing filmas background technologies of polarizing films.

General material properties of thermoplastic resins used in the presentinvention will now be described in the followings.

Thermoplastic resins are roughly classified into two categories, onebeing those which are in a crystallized state having regularly orientedpolymer molecules and the other being those in an amorphous ornon-crystallizable state having polymer molecules which not regularlyoriented or only in part regularly oriented. The former is referred asin a crystallized state and the latter in an amorphous ornon-crystallizable state. Correspondingly, a thermoplastic resin havinga nature of forming a crystallized state is referred as a crystallizableresin, and that which does not have such a nature is referred as anon-crystallizable resin. On the other hand, regardless whether it iscrystallizable or not, a resin which is not in a crystallized state orwhich has not been crystallized is referred as amorphous or non-crystalresin. Herein, the term “amorphous” or “non-crystal” resin is used in adifferent meaning from a “non-crystallizable” resin that does not take acrystallized state.

Crystallizable resins include, for example, olefin type resins includingpolyethylene (PE) and polypropylene (PP), and ester type resinsincluding polyethylene terephthalate (PET) and polybutyleneterephthalate (PBT). One of the characteristics of such crystallizableresin is that heating or stretching generally causes polymer moleculesbeing oriented and crystallization being progressed. Physical propertiesof such resins vary according to the extent of crystallization. On theother hand, even in the case of crystallizable resins such as PP andPET, it is possible to suppress crystallization by inhibiting polymermolecules being oriented through application of heat or stretching. SuchPP and PET in which crystallization is thus suppressed are respectivelyreferred as non-crystallizable polypropylene and non-crystallizablepolyethylene terephthalate, and they are respectively generally referredas non-crystallizable olefin type resin and non-crystallizable estertype resin.

In case of PP, for example, it is possible to produce anon-crystallizable PP in which crystallization is suppressed byproviding the PP with atactic structure having no stereoscopicregularity. Further, in case of PET, for example, it is possible toproduce a non-crystallizable PET by copolymerizing modifier group suchas isophthalic acid or 1,4-cyclohexanedimethanol as a polymerizingmonomer, or by copolymerizing molecules that inhibit crystallization ofPET.

General description will now be made on optical properties of polarizingfilm that may be used in a large sized display.

The term “optical properties” of a polarizing film is used in short tomean polarizing performance represented by polarization rate P andsingle layer transmittance T. In general, the polarization rate P andthe single layer transmittance T of a polarizing film are in trade-offrelationship. In a T-P diagram, there are plotted a plurality of valuesof the two optical factors. In a T-P diagram, it is interpreted that thepolarizing performance of a polarizing film is superior if the singlelayer transmittance is higher (to the right of the diagram) and thepolarization rate is higher (to the top of the graph) as indicated bythe plotted line.

Reference is now made to the diagram in FIG. 3. It is to be noted thatan ideal optical property is a case where T is 50% and P is 100%. Notethat it is easier to increase the value of P with a low value of T, andit is difficult to increase the value of P with a high value of T.Further, referring to FIG. 4, there is shown a solid line drawn alongplots to define a range in terms of the single layer transmittance T andthe polarization rate P meaning that the values of the single layertransmittance T and the polarization rate P within the range meetspecifically “required performance” providing a display contrast ratioof 1000:1 or higher and the maximum luminance of 500 cd/m² or higher.These specific values are considered to be, currently or even in future,optical properties required for a polarizing film for a large sizedisplay element. An ideal value of the single layer transmittance T is50%, but when light transmits through a polarizing film, a part of lightis reflected at a boundary between the polarizing film and air. Takingsuch reflection into consideration, it is noted that the single layertransmittance T is reduced by an extent corresponding to the portion ofthe reflected light, and the maximum attainable value of the singlelayer transmittance T may be 45 to 46%.

On the other hand, the polarization rate P may be converted to acontrast ratio (CR) of a polarizing film. For example, the polarizationrate P of 99.95% corresponds to the contrast ratio CR of 2000:1 of apolarizing film. When this polarizing film is used in each of theopposite sides of a cell for a liquid-crystal television, the displayedimage contrast ratio CR may be 1050:1. Such decrease in the displayedimage contrast ratio CR as compared with the polarizing film contrastratio CR is caused by the fact that depolarization occurs within thecell. Depolarization is caused by scatter and/or reflection of lightwhich occur at the pigment in color filters, liquid-crystal moleculelayer and a thin-film transistor (TFT) when the light is passed throughthe polarizing film on the backlight side and through the cell,resulting in a change in polarizing state of a part of the light. Thecontrast ratio CR of a liquid-crystal display television will becomebetter and easier to observe the displayed image with increase in thecontrast ratio CR of the polarizing film and that of the display.

By the way, the contrast ratio of a polarizing film is defined as avalue of a parallel transmittance (Tp) divided by a cross transmittance(Tc). On the other hand, the contrast ratio of a display can be definedas a value of the maximum intensity of brightness divided by the minimumbrightness. The minimum brightness is the one in a black screen, and inthe case of a liquid-crystal display television under a general viewingenvironment, the required value for the minimum brightness is 0.5 cd/m²or lower. With the minimum brightness higher than the value, colorreproducibility of the liquid-crystal display may be reduced. Themaximum brightness is the one under a display of white screen, and adisplay with the maximum brightness or luminance in a range of 450 to550 cd/m² is used for a liquid-crystal display television under ageneral viewing environment. With the maximum brightness or luminancelower than the value, visibility of the liquid crystal display may bereduced since the display may become dark to an unacceptable level.

Performance required for a display in a liquid-crystal television havinga large size display element includes the display contrast ratio of1000:1 or higher and the maximum brightness or luminance of 500 cd/m² orhigher. These factors are referred as “required performance.” The line 1(T<42.3%) and the line 2 (T≧42.3%) in FIG. 4 are drafted along points oflimit values of polarizing performance of a polarizing film necessary toachieve the required performance. These lines have been determined withthe following simulations based on combinations of polarizing films on abacklight side and a viewing side shown in FIG. 5.

Contrast ratio and maximum brightness or luminance of a display for aliquid-crystal display television are calculated based on the intensityof light from the illumination light source (the backlight unit), thetransmittance of two polarizing films, one on the backlight side and theother on the viewing side, the transmittance of cells, the polarizationrate of the two polarizing films, one on the backlight side and theother on the viewing side, and the depolarization ratio of the cells.The lines 1 and 2 in FIG. 4 designate the boarder of the requiredperformance and derived based on basic values including the intensity ofthe illumination light source (10,000 cd/m²), the transmittance (13%)and the depolarization ratio (0.085%) of the cells used in aconventional liquid-crystal display television, providing several pairsof polarizing films with various polarizing performance, and performingcalculations to obtain the contrast ratio CR and the maximum brightnessfor each pair of the polarizing films in the display for a conventionalliquid-crystal display television. It is to be understood that anypolarizing film which does not reach the line 1 and/or the line 2 hasthe contrast ratio CR lower than 1000:1 and the maximum brightness lowerthan 500 cd/m². The followings are the equations used for thecalculation.

Equation 1 is the one for determining the contrast ratio CR of adisplay. Equation 2 is for determining the maximum brightness of adisplay. Equation 3 is for determining the dichroic ratio of apolarizing film.CRD=Lmax/Lmin  Equation 1Lmax=(LB×Tp−(LB/2×k1B×DP/100)/2×(k1F−k2F))×Tcell/100  Equation 2R=A _(k2) /A _(k1)=log(k2)/log(k1)=log(Ts/100×(1−P/100)/T_(PVA))/log(Ts/100×(1+P/100)/T _(PVA))  Equation 3

Where;

Lmin=(LB×Tc+(LB/2×k1B×DP/100)/2×(k1F−k2F))×Tcell/100

Tp=(k1B×k1F+k2B×k2F)/2×T_(PVA)

Tc=(k1B×k2F+k2B×k1F)/2×T_(PVA)

k1=Ts/100×(1+P/100)/T_(PVA)

k2=Ts/100×(1−P/100)/T_(PVA)

CRD: contrast ratio of the display

Lmax: maximum brightness or luminance of the display

Lmin: minimum brightness or luminance of the display

DR: dichroic ratio of the polarizing film

Ts: single layer transmittance of the polarizing film

P: polarization rate of the polarizing film

k1: first primary transmittance

k2: second primary transmittance

k1F: k1 of the polarizing film on the viewing side

k2F: k2 of the polarizing film on the viewing side

k1B: k1 of the polarizing film on the backlight side

k2B: k2 of the polarizing film on the backlight side

A_(k1): absorbance rate in the direction of transmission axis of thepolarizing film

A_(k2): absorbance rate in the direction of absorption axis of thepolarizing film

LB: intensity of illumination light from the illumination light source(10,000 cd/m²)

Tc: cross transmittance of polarizing films (a combination comprising aviewing side polarizing film and a backlight side polarizing film)

Tp: parallel transmittance of polarizing films (a combination comprisinga viewing side polarizing film and a backlight side polarizing film)

Tcell: transmittance of cell (13%)

DP: depolarization ratio of cell (0.085%)

T_(PVA): transmittance of a PVA film having no iodine impregnatedtherein (0.92)

The line 1 in FIG. 4 (T<42.3%) can be derived based on the polarizingperformance of polarizing films belonging to group 3 shown in FIG. 5.Referring to the group 3 shown in FIG. 5, it is noted that a polarizingfilm D designated by a plot D (a white circle) has the polarizingperformance represented by coordinates (T, P)=(42.1%, 99.95%), and twosuch polarizing film can be paired for use at respective ones of thebacklight side and the viewing side of a display for a liquid-crystaldisplay television to satisfy the required performance.

However, even in the case of those belonging to the same group 3, it isto be noted that the other three polarizing films designated as apolarizing film A (40.6%, 99.998%), a polarizing film B (41.1%, 99.94%)and a polarizing film C (41.6%, 99.98%) have transmittance rate lowerthan that of the polarizing film D, so that if two of such polarizingfilms are paired for use in both the backlight side and the viewingside, the required performance cannot be satisfied. When one of thepolarizing films A, B and C is used on either one of the backlight sideor the viewing side, it is required that the polarizing film on theother side has a higher single layer transmittance T than the group 3polarizing film and the polarization rate P of 99.9% or higher, such asa polarizing film E in the group 4, a polarizing film F in the group 5or a polarizing film G in the group 7 in order to attain the requiredperformance.

The properties of the polarizing films belonging to the groups 1 to 7are calculated in accordance with the Equation 3. Use of the Equation 3allows for calculating the single layer transmittance T and thepolarization rate P based on the dichroic ratio (DR) which can beconsidered as an index of the polarizing performances of a polarizingfilm. The dichroic ratio is the absorbance rate in the direction of theabsorption axis of a polarizing film divided by the absorbance rate inthe direction of the transmission axis thereof. It is to be noted thatwith higher value of this ratio it is possible to attain betterpolarizing performance. For example, polarizing films in the group 3 arethose having polarizing performance where the dichroic ratio is about94. It means that any polarizing films with lower DR than this value donot satisfy the required performance.

If a polarizing film, such as a polarizing film H (41.0%, 99.95%) in thegroup 1 or a polarizing film J (42.0%, 99.9%) in the group 2, havinginferior polarizing performance than the polarizing films in the group3, is used as a polarizing film on either one of the backlight side orthe viewing side, it is clear from the Equation 1 and the Equation 2that a polarizing film, such as a polarizing film I (43.2%, 99.95%) inthe group 6 or a polarizing film K (42.0%, 99.998%) in the group 7,having superior polarizing performance than the polarizing films in thegroup 3, has to be used on the other side to satisfy the requiredperformance.

The polarizing performance of either one of the polarizing films on thebacklight side or the viewing side have to be better than that of thepolarizing films in the group 3 to satisfy the required performance of adisplay for a liquid-crystal display television. The line 1 (T<42.3%) inFIG. 4 indicates the lower limit of the polarizing performance, and theline 2 (T≧42.3%) indicates the lower limit of the polarization rate P.If a polarizing film with the polarization rate P of 99.9% or lower isused as a polarizing film on either one of the backlight side or theviewing side, the required performance cannot be satisfied even by usinga polarizing film with the best possible polarizing performance on theother side.

In conclusion, in order to satisfy polarizing performance required for adisplay of a liquid-crystal display television using a large sizedisplay element, the polarizing performance of the polarizing film oneither one of the backlight side or the viewing side should be at leastin the range represented by the line 1 (T<42.3%) and the line 2(T≧42.3%), and more specifically, the polarizing performance should bebetter than that of the polarizing films in the group 3, and thepolarization rate should be 99.9% or higher.

Further, descriptions will now be made with respect to the method formanufacturing a polarizing film consisting of a PVA type resin using athermoplastic resin substrate that a first and a second insolubilizationin the embodiments of the present invention are considered to be partsof the measures for dealing with important technical challenges.

It is to be noted that it would not be an easy task to have iodineimpregnated in a PVA type resin layer without having the PVA type resinlayer included a stretched intermediate (or, a stretched laminate) beingdissolved in a dyeing solution. It is an important technical challengein the manufacture of a polarizing film to have iodine impregnated in aPVA type resin layer of a decreased thickness. Usually, the amount ofiodine impregnated in the PVA type resin layer is controlled by using aplurality of dyeing solutions with different iodine concentration in arange of 0.12 to 0.25 wt % so that the dyeing process is carried out fora constant immersing time. With such usual dyeing process in themanufacture of a polarizing film, the PVA type resin layer can bedissolved to such an extent that dyeing becomes no longer possible.Herein, the term “concentration” means the rate of composition inrelation to a total amount of solution. Further, the term “iodineconcentration” means the rate of iodine in relation to the total amountof solution, and does not include amount of iodine content added as, forexample, potassium iodide. Hereinafter, the terms “concentration” and“iodine concentration” are used in the same meanings as above.

The aforementioned technical challenge has been solved by raising theiodine concentration in the dichroic material to 0.3 wt % or higher asis clear from the experimental results shown in FIG. 6. In particular, astretched laminate comprising a stretched intermediate consisting of aPVA type resin layer is dyed in dyeing solutions with different iodineconcentration, and the immersion time is controlled to form a dyedlaminate comprising dyed intermediate, and then is stretched in boricacid solution to allow for forming each of polarizing films with variouspolarizing properties.

Reference is made to the diagram shown in FIG. 7. In FIG. 7, it has beenverified that there is no meaningful difference in the polarizingperformance between polarizing films formed in the solutions ofdifferent iodine concentrations of 0.2 wt %, 0.5 wt % and 1.0 wt %. Inthis regard, in the manufacture of a dyed laminate including a dyedintermediate, it is preferable for accomplishing dyeing of excellentuniformity in a stable manner to use a solution of decreased iodineconcentration so as to secure a stable immersion time, rather than touse a solution of increased iodine concentration for carrying out dyeingprocess within a short immersion time.

Reference is now made to the diagram in FIG. 8. It is to be noted thatthe first and second insolubilization processes in the embodiments ofthe present invention (hereinafter referred as “the first and the secondinsolubilization processes”) both have effects on the optical propertiesof the finally manufactured polarizing films. FIG. 8 is considered asshowing results of analysis relating to the effects of the first and thesecond insolubilization processes on the PVA type resin layer havingdecreased thickness. FIG. 8 has been drafted by plotting opticalproperties of each of polarizing films manufactured based on theexamples 1 to 4 which satisfy the required performance for a display fora liquid-crystal display television using a large size display element.

The example 1 shows the optical properties of the polarizing filmmanufactured without adopting the first and the second insolubilizationprocesses, the example 2 shows the optical properties of the polarizingfilm manufactured without adopting the first insolubilization processbut adopting the second insolubilization process, the example 3 showsthe optical properties of the polarizing film manufactured with thefirst insolubilization process but without the second insolubilizationprocess, and the example 4 shows the optical properties of thepolarizing film manufactured with both the first and the secondinsolubilization processes.

In the embodiments of the present invention, a polarizing film thatsatisfies the required performance may be manufactured without the firstand the second insolubilization processes. However, as clearly shown inFIG. 8, the optical properties of the example 1, manufactured withoutthe first and the second insolubilization processes, are inferior tothose of the polarizing films in accordance with the examples 2 to 4.Comparing the optical properties of respective ones of the examples, itwill be noted that the optical properties of the example 4 are the best,those of the example 2 are the second best, then followed by the example3 and then the example 1. In each of the examples 1 and 2, a dyeingsolution with the iodine concentration of 0.3 wt % and the potassiumiodide concentration of 2.1 wt % is used. In contrast, in the examples 3and 4, there have been used a plurality of dyeing solutions in whichiodine concentrations have been varied in a range of 0.12 to 0.25 wt %and potassium iodide concentration in a range of 0.84 to 1.75 wt %. Adecisive difference between the group of the examples 1 and 3 and thegroup of the examples 2 and 4 is that the dyed intermediate of theformer group has not been insolubilized, but the dyed intermediate ofthe latter group has been insolubilized. For the example 4, theinsolubilization processes have been applied not only to the dyedintermediate before the in-boric-acid-solution stretching but also tothe stretched intermediate before dyeing. It is to be noted that throughthe first and the second insolubilization processes, furtherimprovements in the optical properties of the polarizing films have beenaccomplished.

It is to be noted that the mechanism for improving optical properties ofa polarizing film does not owe to the iodine concentration in the dyeingsolution as is clear in FIG. 7. It is understood that it is the resultof the first and the second insolubilization processes. This finding maybe regarded as a third technical challenge and the solution thereto inthe manufacturing process of the present invention.

According to the embodiments of the present invention, the firstinsolubilization process is adopted to insolubilize the PVA type resinlayer of a decreased thickness included in the stretched intermediate(or the stretched laminate). On the other hand, the secondinsolubilization process included in the cross-linking process is forstabilizing iodine impregnated in the PVA type resin layer in the dyedintermediate (or a dyed laminate) so that the iodine is prevented frombeing eluted during the in-boric-acid-solution stretching under thesolution temperature of 75° C. in a later process, and forinsolubilizing the PVA type resin layer of decreased thickness.

It should however be noted that, if the second insolubilization processwas omitted, the iodine impregnated in the PVA type resin layer wouldpossibly be eluted during the in-boric-acid-solution stretching underthe solution temperature of 75° C., so that the PVA type resin layerwould possibly be dissolved. Such elution of iodine and dissolution ofthe PVA type resin layer may be avoided by lowering boric acid solutiontemperature. For example, it is required to have a dyed intermediate (ora dyed laminate) stretched while it is immersed in the boric acidsolution under the solution temperature lower than 65° C. However, suchlowered solution temperature may result in a plasticizing function ofwater being utilized only to an insufficient extent, so that the PVAtype resin layer included in the dyed intermediate (or the dyedlaminate) may not be softened to a satisfactory level. Thus, there maybe a risk that stretchability of the intermediate may be decreased to alevel that breakage of the dyed intermediate (or the dyed laminate) mayoccur during the in-boric acid solution stretching. This will mean as amatter of fact that an intended total stretching ratio of the PVA typeresin layer cannot be attained.

(General Description of the Manufacturing Process)

Reference is made to FIG. 9. FIG. 9 is a schematic drawing showing oneexample of manufacturing process for an optical film laminate 10comprising a polarizing film 3 in which an insolubilization process isnot carried out. Here, description will be made on the method formanufacturing an optical film laminate 10 comprising a polarizing film 3in accordance with the example 1.

A non-crystallizable ester type thermoplastic resin substrate has beenprovided in the form of a continuous web of substrate comprisingisophthalic acid-copolymerized polyethylene terephthalate (hereinafterreferred as non-crystallizable PET) including 6 mol % of isophthalicacid copolymerized therein. A laminate 7 has been produced from thecontinuous web of non-crystallizable PET substrate 1 having theglass-transition temperature of 75° C., and a PVA layer 2 having theglass-transition temperature of 80° C. in accordance with the followingprocedures.

(Laminate Manufacturing Process (A))

First, a non-crystallizable PET substrate 1 having a thickness of 200μm, and a PVA solution has been prepared. The PVA solution had a PVAconcentration of 4 to 5 wt % and made from powders of PVA having adegree of polymerization of 1000 or higher and a degree ofsaponification of 99% or higher, the powders being dissolved in water toprepare the solution. Then, using a laminate manufacturing apparatus 20comprising a coating unit 21, a drying unit 22 and a surface modifyingapparatus 23, the PVA solution is coated on the non-crystallizable PETsubstrate 1 with a thickness of 200 μm, and dried at a temperature of 50to 60° C., to form a 7 μm-thick PVA layer 2 on the non-crystallizablePET substrate 1. Hereinafter, is the product formed as above is referredas “a laminate 7 comprising a 7 μm-thick PVA layer formed on anon-crystallizable PET substrate,” or “a laminate 7 comprising a 7μm-thick PVA layer,” or simply as “a laminate 7.”

The laminate 7 comprising a PVA layer is used to finally manufacture a 3μm-thick polarizing film 3 through following processes including a2-stage stretching including a preliminary in-air stretching and anin-boric-acid-solution stretching.

(Preliminary In-Air Stretching Process (B))

In a first stage or preliminary in-air stretching process (B), thelaminate 7 comprising the 7 μm-thick PVA layer 2 is integrally stretchedwith the non-crystallizable PET substrate 1 to form “a stretchedlaminate 8” including a 5 μm-thick PVA layer 2. Particularly, using apreliminary in-air stretching apparatus 30 comprising a stretching unit31 located in an oven 33, the laminate 7 including the 7 μm-thick PVAlayer 2 is subjected to an end-free uniaxial stretching by thestretching unit 31 in the oven 33 at a stretching temperature of 130° C.to a stretching ratio of 1.8, to form the stretched laminate 8. At thisstage, the stretched laminate 8 may be wound into a roll 8′ with awinding apparatus 32 provided in relation to the oven 33.

End-free stretching and fixed-end stretching will now be outlined. Whena continuous film is stretched in the feeding direction, the filmshrinks in the direction orthogonal to the stretching direction, i.e. inwidth-wise direction. The end-free stretching is a stretching process inwhich no restriction incurred against the shrinkage. A longitudinaluniaxial stretching is a method of stretching wherein a stretching forceis applied only in the longitudinal direction. The end-free uniaxialstretching is generally compared with a fixed-end uniaxial stretching inwhich shrinkage occurring in the direction orthogonal to the stretchingdirection is restricted. Through the end-free uniaxial stretching, the 7μm-thick PVA layer 2 included in the laminate 7 is stretched into a 5μm-thick PVA layer 2 having PVA molecules oriented therein.

(Dying Process (C))

A dyeing process (C) is then carried out to produce a dyed laminate 9having a dichroic material comprised of iodine impregnated in the 5μm-thick PVA layer 2 which includes PVA molecules oriented therein. Morespecifically, there has been produced a dyed laminate 9 in which theoriented PVA layer 2 of the stretched laminate 8 includes iodineimpregnated therein, using a dyeing apparatus 40 comprising a dye pool42 of a dyeing solution 41 containing iodine and potassium iodide, tohave the stretched laminate 8 unrolled from the roll 8′ mounted on afeeding apparatus 43 provided in relation to the dyeing apparatus 40 andimmersed for an appropriate time in the dyeing solution at a solutiontemperature of 30° C., so that a resultant polarizing film 3 provided bythe PVA layer has a single layer transmittance (T) of 40 to 44%.

In the above process, the dyeing solution 41 contains water as a solventand iodine with a concentration of 0.30 wt % in order that the PVA layer2 included in the stretched laminate 8 will not be dissolved. Inaddition, the dyeing solution 41 contains potassium iodide of 2.1 wt %for making it possible to dissolve iodine in water. The ratio ofconcentration of iodine to that of potassium iodide is 1:7. Describingin more detail, the laminate 8 is immersed for 60 seconds in the dyeingsolution 41 with iodine concentration of 0.30 wt % and potassium iodideconcentration of 2.1 wt % to form the dyed laminate 9 having iodineimpregnated in the 5 μm-thick PVA layer 2 in which PVA molecules areoriented therein. In the example 1, immersion time of the stretchedlaminate 8 in the dyeing solution 41 with iodine concentration of 0.30wt % and potassium iodide concentration of 2.1 wt % is varied forcontrolling the impregnated amount of iodine so that dyed laminates 9having several different values of the single layer transmittance T andthose of the polarization rate P are produced within the range of thesingle layer transmittance T of 40 to 44%.

(In-Boric-Acid-Solution Stretching Process (D))

In a second stage or in-boric-acid-solution stretching process (D), thedyed laminate 9 including the PVA layer 2 having iodine impregnatedtherein in an oriented state is further stretched to form an opticalfilm laminate 10 including the PVA layer having iodine impregnatedtherein in an oriented state which provides a 3 μm-thick polarizing film3. Particularly, using an in-boric-acid-solution stretching apparatus 50comprising a boric acid solution pool 52 of boric acid solution 51 and astretching unit 53, the dyed laminate 9 continuously delivered from thedyeing apparatus 40 is immersed in the boric acid solution 51 containingboric acid and potassium iodide at a solution temperature of 65° C.,then is fed to the stretching unit 53 arranged in thein-boric-acid-solution stretching apparatus 50 for an end-free uniaxialstretching, to a stretching ratio of 3.3, to form the optical filmlaminate 10.

Describing in more detail, the boric acid solution 51 has been providedin a form containing 4 parts in weight of boric acid with respect to 100parts in weight of water, and 5 parts in weight of potassium iodide withrespect to 100 parts in weight of water. In the process, the dyedlaminate 9 included amount of iodine impregnated therein is firstlyimmersed for 5 to 10 seconds in the boric acid solution 51. The dyedlaminate 9 is then passed as it is through a plurality of pairs of rollsdriven with different peripheral speeds so as to constitute thestretching unit of the in-boric-acid-solution stretching apparatus 50for carrying out the end-free uniaxial stretching to a stretching ratioof 3.3 in 30 to 90 seconds. This stretching process has been effectiveto change the PVA layer in the dyed laminate 9 to a 3 μm-thick PVA layerhaving the iodine impregnated therein in a high-order oriented state inone direction in the form of a polyiodide ion complex. The PVA layerprovides the polarizing film 3 in the optical film laminate 10.

As described above, in the example 1, there has been produced an opticalfilm laminate 10 comprising a 3 μm-thick PVA layer integrally stretchedwith a non-crystallizable PET substrate, starting with a laminate 7comprising a 7 μm-thick PVA layer 2 formed on the non-crystallizable PETsubstrate 1, by subjecting it to a preliminarily in-air stretching at astretching temperature of 130° C. to form a stretched laminate 8, thensubjecting the stretched laminate 8 to a dyeing process to thereby forma dyed laminate 9, the dyed laminate 9 being then stretched in boricacid solution at a temperature of 65° C., so that the total stretchingratio becomes 5.94. Such 2-stage stretching allows for high-orderorientation of the PVA molecules in the PVA layer 2 formed on thenon-crystallizable PET substrate 1 to form an optical film laminatecomprising a 3 μm-thick PVA layer providing a polarizing film 3 havingiodine impregnated therein during dyeing process with a high-orderorientation in the form of a polyiodide ion complex. Preferably, theformed optical film laminate 10 is subjected to subsequent cleaning,drying and transferring processes to obtain a finished product. Thedetails of processes for the cleaning (G), drying (H) and transferring(I) will be described in association with a manufacturing processincorporating insolubilization process in the example 4.

(General Description of Other Manufacturing Processes)

Reference should now be made to FIG. 10. FIG. 10 is a schematicillustration of a method for manufacturing the optical film laminate 10including the polarizing film 3 adopting an insolubilization process.Here, descriptions will be made with respect to a manufacturing processof the optical film laminate 10 including the polarizing film 3 inaccordance with the example 4. As apparent in FIG. 10, the manufacturingprocess for the example 4 may be understood as being the onecorresponding to the process for the example 1, but the firstinsolubilization is additionally incorporated before the dyeing processand the cross-linking process including the second insolubilizationprocess before the in-boric-acid-solution stretching. In the presentmethod, it can be interpreted that the laminate manufacturing process(A), the preliminary in-air stretching process (B), the dyeing process(C) and the in-boric-acid-solution stretching process (D) are identicalto those in the manufacturing process of the example 1, except adifference in the temperature of the boric acid solution for thein-boric-acid-solution stretching. Thus, descriptions on these processesare only briefly be made, and the first insolubilization process beforedying process and the cross-linking process including the secondinsolubilization process before in-boric-acid-solution stretching willbe primarily described.

(First Insolubilization Process (E))

The first insolubilization process is an insolubilization process (E)carried out prior to the dyeing process (C). As in the manufacturingprocess in accordance with the example 1, the laminate 7 comprising the7 μm-thick PVA layer 2 formed on the non-crystallizable PET substrate isproduced in the laminate manufacturing process (A), then the laminate 7including the 7 μm-thick PVA layer 2 is subjected to an in-airstretching process as shown by the preliminary in-air stretching process(B) to form the stretched laminate 8 including the 5 μm-thick PVA layer2. Subsequently, the stretched laminate 8 delivered from the roll 8′mounted on the feeding apparatus 43 is insolubilized to form theinsolubilized stretched laminate 8″. As a matter of fact, theinsolubilized stretched laminate 8″ includes an insolubilized PVA layer2, is the laminate 8″ being hereinafter referred as—a insolubilizedstretched laminate 8″—.

More specifically, use is made of an insolubilizing apparatus 60containing a boric acid insolubilizing solution 61, and the stretchedlaminate 8 is immersed for 30 seconds in the boric acid insolubilizingsolution 61 under a solution temperature of 30° C. The boric acidinsolubilizing solution 61 used in this process contains 3 parts inweight of boric acid with respect to 100 parts in weight of water(hereinafter referred as “boric acid insolubilizing solution”). Thisprocess aims at insolubilizing the 5 μm-thick PVA layer included in thestretched laminate 8 so that the PVA layer is prevented from beingdissolved at least during the immediately following dyeing process (C).

After insolubilizing the stretched laminate 8, different dyeingsolutions has been prepared with iodine concentration varying in a rangeof 0.12 to 0.25 wt %, in contrast to the case of the example 1, andvarious dyed laminates 9 having different values of the singletransmittance and those of the polarization rate have been produced,using these dyeing solutions and maintaining the immersion time of theinsolubilized stretched laminate 8″ in the dyeing solution constant forcontrolling the amount of the impregnated iodine so that the singletransmittance of the finally formed polarizing film becomes 40 to 44%.Even after such immersing in the dyeing solutions with iodineconcentration of 0.12 to 0.25 wt %, the PVA layers in the insolubilizedstretched laminates 8″ have not been dissolved.

(Cross-Linking Process Including Second Insolubilization (F))

Cross-linking process can be interpreted as including a function of thesecond insolubilization in view of the objects described in thefollowings. The cross-linking process aims at, firstly making the PVAlayer in the dyed laminate 9 insoluble during the followingin-boric-acid-solution stretching process (D), secondly stabilizing thedye impregnated in the PVA layer so that iodine in the PVA layer willnot be eluted, and thirdly forming junction points by cross-linkingmolecules in the PVA layer. The second insolubilization is realized bythe first and the second aims.

Cross-linking (F) is a process performed prior to thein-boric-acid-solution stretching process (D). The dyed laminate 9formed in the dyeing process (C) is cross-linked to form a cross-linkeddyed laminate 9′ that includes a cross-linked PVA layer 2. Specifically,use is made of a cross-linking apparatus 70 containing a solution 71which includes iodine and potassium iodide (hereinafter referred as“boric acid cross-linking solution”), and the dyed laminate 9 isimmersed for 60 seconds in the boric acid cross-linking solution 71under a solution temperature of 40° C. to have the PVA moleculescross-linked in the PVA layer having iodine impregnated therein, toyield the cross-linked dyed laminate 9′. The boric acid cross-linkingsolution 71 in this process contains 3 parts in weight of boric acidwith respect to 100 parts in weight of water and 3 parts in weight ofpotassium iodide with respect to 100 parts in weight of water.

In the in-boric acid solution stretching process (D), the cross-linkeddyed laminate 9′ is immersed in the boric acid solution under a solutiontemperature of 75° C. and subjected to an end-free uniaxial stretchingprocess, to a stretching ratio of 3.3, to form the optical film laminate10. Through the stretching process, the PVA layer 2 included in the dyedlaminate 9′ and having iodine impregnated therein has been converted tothe 3 μm-thick PVA layer 2 which includes the impregnated iodine in theform of a polyiodide ion complex oriented in one direction with a highorder orientation rate. This PVA layer provides the polarizing film 3 inthe optical film laminate 10.

The example 4 has been prepared by firstly providing a laminate 7comprising a 7 μm-thick PVA layer 2 formed on a non-crystallizable PETsubstrate 1, then subjecting the laminate 7 to an end-free uniaxialstretching to carry out the preliminary in-air stretching at astretching temperature of 130° C. to the stretching ratio of 1.8 to forma stretched laminate 8. Then, the formed stretched laminate 8 isimmersed in the boric acid insolubilizing solution 61 under a solutiontemperature of 30° C. to insolubilize the PVA layer included in thestretched laminate to form an insolubilized stretched laminate 8″. Theinsolubilized stretched laminate 8″ is immersed in dyeing solutioncontaining iodine and potassium iodide under a solution temperature of30° C. to form a dyed laminate 9 having iodine impregnated in theinsolubilized PVA layer. Then, the dyed laminate 9 comprising the PVAlayer having iodine impregnated therein is immersed for 60 seconds inthe boric acid cross-linking solution 71 under a solution temperature of40° C. to have PVA molecules in the PVA layer having iodine thereincross-linked to form the cross-linked dyed laminate 9′. Subsequently,the cross-linked dyed laminate 9′ is immersed for 5 to 10 seconds in asolution 51 containing boric acid and potassium iodide for carrying outan in-boric-acid-solution stretching at a solution temperature of 75°C., and is subjected to an end-free uniaxial stretching in the solutionfor the in-boric-acid-solution stretching, to a stretching ratio of 3.3,to form the optical film laminate 10.

As described above, the process for the example 4 includes the 2-stagestretching consisting of the elevated temperature in-air stretching andthe in-boric-acid-solution stretching, and the pre-processing consistingof the insolubilization before immersion in the dyeing pool and thecross-linking before the in-boric-acid-solution stretching, so that itis possible to manufacture the optical film laminate 10 in a stablemanner, the laminate 10 including the 3 μm-thick PVA layer whichprovides the polarizing film in which the PVA molecules in the PVA layer2 formed on the non-crystallizable PET substrate 1 are oriented with ahigh-order orientation rate and iodine molecules securely impregnatedamong the PVA molecules through the dyeing process are oriented thereinwith a high-order orientation rate in one direction in the form of anpolyiodide ion complex.

(Cleaning Process (G))

The dyed laminate 9 or the cross-linked dyed laminate 9′ in accordancewith the example 1 or the example 4 is stretched in thein-boric-acid-solution stretching process (D), and then taken out of theboric acid solution 51. The taken out optical film 10 including thepolarizing film 3 is preferably conveyed to a cleaning process (G) as itis. The cleaning process (G) aims at washing out unnecessary residualsdepositing on a surface of the polarizing film 3. The cleaning process(G) may be omitted and the optical film 10 including the polarizing film3 may be directly conveyed to a drying process (H). It should however benoted that, if the optical film laminate 10 is not sufficiently cleaned,boric acid may precipitate on the polarizing film 3 after dryingprocess. Thus, the optical film laminate 10 is conveyed to a cleaningapparatus 80 and immersed for 1 to 10 seconds in a cleaning solution 81containing potassium iodide under a solution temperature of 30° C. suchthat the PVA in the polarizing film 3 does not dissolve. Potassiumiodide concentration in the cleaning solution 81 may be about 0.5 to 10wt %.

(Drying Process (H))

The cleaned optical film laminate 10 is conveyed to a drying process (H)to be dried. Then, the dried optical film laminate 10 which is in theform of a continuous web is taken up by a winding apparatus 91 providedin relation to the drying apparatus 90 to provide a roll of the opticalfilm laminate 10 including the polarizing film 3. Any appropriateprocess, such as natural drying, blow drying and thermal drying, may beadopted for the drying process (H). In both the examples 1 and 4, thedrying process has been performed with warm air at a temperature of 60°C. for 240 seconds in the drying apparatus 90 provided in the oven.

(Laminating and Transferring Process (I))

The optical film laminate 10 comprising the 3 μm-thick polarizing film 3formed on the non-crystallizable PET substrate is wound as a roll of theoptical film laminate 10, and then is subjected to laminating andtransferring steps which are carried out simultaneously in alaminating/transferring process (I) such as a process described in thefollowings. The manufactured polarizing film 3 is of a decreasedthickness by being stretched and may be as thin as 10 μm or less,usually only 2 to 5 μm, such reduced thickness making it difficult tohandle the polarizing film 3 as a single layer. Thus, the polarizingfilm 3 needs to be handled in the form of an optical film laminate 10after it has been formed on the non-crystallizable PET substrate, or, asan optically functional film laminate 11 which is provided by laminatingand transferring the polarizing film to another optically functionalfilm 4 through a bonding agent.

In the laminating/transferring process (I) shown in FIG. 9 or FIG. 10,the optically functional film 4 is laminated to the optical filmlaminate 10 at a side of the polarizing film 3 through a bonding agent,and the non-crystallizable PET substrate is peeled from the polarizingfilm 3. Thus, the polarizing film 3 is transferred to the opticallyfunctional film 4, to form the optically functional film laminate 11which is then taken up into a roll. Specifically, the optical filmlaminate 10 is fed out by a feeding/laminating apparatus 101 included ina laminating/transferring apparatus 100, and laminated to the opticalfilm laminate 10 at a side of the polarizing film 3 through a bondingagent, the polarizing film 3 being then peeled from the optical filmlaminate 10 to have the polarizing film 3 transferred to the opticallyfunctional film 4 by means of a winding/transferring apparatus 102, tothereby form the optically functional film laminate 11.

The optical film laminate 10 taken up into a roll by the windingapparatus 91 in the drying process (H) or the optically functional filmlaminate 11 formed in laminating/transferring process (I) can take widevarieties of structures.

FIG. 11 and FIG. 12 show varieties of structures of the optical filmlaminate 10 or the optically functional film laminate 11 as typicalpatterns 1 to 4.

In FIG. 11 illustrating the patterns 1 and 2, there are shown inschematic sections laminated structures of an optical film laminate 12and an optical film laminate 13 having sectional configurations whichare different from that in the optical film laminate 10. The opticalfilm laminate 12 includes a separator 17 which is laminated on thepolarizing film 3 of the optical film laminate 10 through an adhesiveagent layer 16. As shown in the specific example 1 in FIG. 11, in thecase where the non-crystallizable PET substrate 1 constitutes aprotection film, the laminate 12 may be used as an optical film laminateon either a backlight side or a viewing side of, for example, a displaypanel 200 for an IPS-type liquid-crystal display television. In thiscase, two of the optical film laminates may be attached to both sides ofthe IPS liquid-crystal cell 202 respectively through the adhesive agentlayers 16. In this configuration, a surface treatment layer 201 maygenerally be formed on the viewing side surface of thenon-crystallizable PET substrate 1.

The optical film laminate 13 is constructed to include an opticallyfunctional film 4 which is attached to the polarizing film 3 of theoptical film laminate 10 with a bonding agent layer 18, a separator 17being attached to the optically functional film 4 with an adhesive agentlayer 16. As shown in the specific example 2 in FIG. 11, in the casewhere the optically functional film 4 is a biaxial phase difference film301 with refraction indices nx, ny and nz along three orthogonal axeshave relation of nx>ny>nz, the optical film laminate 13 may be used asan optically functional film laminate for use either on a backlight sideor a viewing side of, for example, a display panel 300 for a VA-typeliquid-crystal display television. In this case, the optical filmlaminates are attached to both sides of the VA type liquid-crystal cell302 respectively with the adhesive agent layers 16. In thisconfiguration, a surface treatment layer 201 may generally be formed onthe viewing side surface of the non-crystallizable PET substrate 1. Boththe optical film laminate 12 and the optical film laminate 13 arecharacterized in that the non-crystallizable PET substrate 1 is notpeeled off the polarizing film 3 but is used as, for example, aprotection film of the polarizing film 3.

In FIG. 12 illustrating the patterns 3 and 4, there are shown inschematic sections structures of an optical film laminate 14 and anoptical film laminate 15 which have sectional configurations differentfrom that of the optical film laminate 11. The optical film laminate 14includes a polarizing film 3 which has in advance been transferred tothe optically functional film 4 by having the non-crystallizable PETsubstrate 1 peeled therefrom and attached to the optically functionalfilm 4 with a bonding layer 18. The optical film laminate 14 furtherincludes a separator 17 which is attached through an adhesive agentlayer 16 to the surface of the polarizing film 3 opposite to the surfacefrom which the non-crystallizable PET substrate 1 has been peeled. Asshown in the specific example 3 in FIG. 12, in the case where theoptically functional film 4 is comprised of a protection film made of aTAC film 401, the laminate 14 may be used as an optically functionalfilm laminate for use either on a backlight side or a viewing side of,for example, a display panel 400 for an IPS-type liquid-crystal displaytelevision. In this case, the optical film laminates attached to bothsides of the IPS liquid-crystal cell 402 respectively with the adhesiveagent layers 16. In this configuration, a surface treatment layer 201may generally be formed on the viewing side surface of the TAC film 401.

The optical film laminate 15 includes a second optically functional film5 which is attached through a second bonding agent 18 to the surface ofthe polarizing film 3 opposite to the surface from which thenon-crystallizable PET substrate 1 has been peeled in transferring thepolarizing film 3 to the optically functional film 4 using a firstbonding agent 18 to form a laminate, a separator 17 being attached tothus formed laminate with the adhesive agent 16. As shown in thespecific example 4 in FIG. 12, in the case where the opticallyfunctional film 4 is comprised of a TAC film 401 and the secondoptically functional film 5 is a biaxial phase difference film 501having refraction indices nx, ny and nx along three orthogonal axes witha relation of nx>nz>ny, the optical film laminate 15 may be used as anoptically functional film laminate for use on a backlight side of, forexample, a display panel 500 for an IPS-type liquid-crystal displaytelevision. In this case, such optical film laminate is attached to thebacklight side of the IPS liquid-crystal cell 502 with the adhesiveagent layer 16.

The optically functional film laminate 15 may further be used as ananti-reflection film (a circular polarizing plate) for preventingsurface reflection in a display apparatus or interface reflection at aninterface of members in the display apparatus, by forming the secondoptically functional film as a λ/4 phase difference film 602.Particularly, in the case where the optically functional film 4 is inthe form of an acrylic resin film 601, where the second opticallyfunctional film 5 constitutes a λ/4 phase difference film 602, or wherethe polarizing film 3 and the λ/4 phase difference film are laminatedwith a lamination angle between the absorption axis of the polarizingfilm 3 and the slow axis of the λ/4 phase difference film being set to45 degrees, then the laminate 15 may be used as an anti-reflection filmof, for example, an organic electroluminescence (EL) display 600 asshown in the specific example 5 in FIG. 12. In this case, such opticallyfunctional film may be attached to the viewing side of the organic ELpanel 603 with the adhesive agent layer 16. In this configuration, asurface treatment layer 201 may generally be formed on the viewing sideof the acrylic resin film 601.

Both the optical film laminate 14 and the optical film laminate 15 arecharacterized in that the laminate used in the laminate is the one fromwhich the non-crystallizable PET substrate 1 has been peeled off at thesame time when the polarizing film 3 is transferred to the opticallyfunctional film 4.

It should further be noted that the optically functional film in each ofthe layers constituting respective ones of the optically functional filmlaminates 11, 14 and 15, and the optical film laminates 12 and 13 is notlimited to those described above. The optically functional film maycomprise anyone of a TAC film or a polarizing film protection filmcontaining acrylic resin, any phase difference film including a biaxialphase difference film (for example, a film having refraction indices nx,ny and nz with a relation of nx>ny>nz, or nx>nz>ny), a λ/4 phasedifference film, a λ/2 phase difference film, a positive-dispersionphase difference film, a flat-dispersion phase difference film, areverse-dispersion phase difference film, a brightness enhancement film,and a diffusion film. In addition, a plurality of those films may belaminated together for use. The adhesive agent layer 16 or the bondingagent layer 18 may be of any appropriate adhesive agent or bondingagent. Representatively, the adhesive agent layer may be of an acrylicadhesive agent and the bonding agent layer may be of a vinyl alcoholtype bonding agent.

(Optical Properties of Polarizing Film Manufactured Under VariousConditions)

(1) Improvement in the Optical Properties of the Polarizing Film withInsolubilization (Examples 1 to 4)

It has been clarified in the descriptions with reference to FIG. 8 that,each of the polarizing films manufactured based on the examples 1 to 4has been effective to overcome the technical objects of the presentinvention, and that the optical properties of each of the polarizingfilms satisfy the required performance for a display of liquid-crystaldisplay television using a large size display element. Further, as isclear from the diagram in FIG. 8, the optical properties of thepolarizing film of the example 1 without insolubilization are inferiorto any of optical properties of the polarizing films of the examples 2to 4 with the first and/or the second insolubilization. The opticalproperties of the examples have the following relation in terms ofsuperiority: The example 4 with the first and the secondinsolubilization>the example 2 with only the second insolubilization>theexample 3 with only the first insolubilization>the example 1. It is tobe further noted that improvements can be accomplished in the opticalproperties of the polarizing film or those of the optical film laminateincluding the polarizing film, by applying the first and/or the secondinsolubilization process in addition to the manufacturing process of theoptical film laminate 10.

(2) Influence of the Thickness of the PVA Type Resin Layer on theOptical Properties of the Polarizing Film (Example 5)

In the example 4, the 7 μm-thick PVA layer has been stretched to finallyobtain the 3 μm-thick PVA layer in the optical film laminate, whereas inthe example 5, the 12 μm-thick PVA layer has been stretched to finallyobtain the 5 μm-thick PVA layer in the optical film laminate. Thispolarizing film in the example 5 has been manufactured under the sameconditions as in the example 4 except the thickness.

(3) Influence of the Difference in Thickness of the Non-CrystallizablePet Substrate on the Optical Properties of the Polarizing Film (Example6)

In the example 4, the non-crystallizable PET substrate has includedisophthalic acid copolymerized to PET, whereas in the example 6, use hasbeen made of a non-crystallizable PET substrate including1,4-cyclohexanedimethanol copolymerized to PET as a modified base. Thispolarizing film was manufactured under the same conditions as in theexample 4 except the modified base.

Reference is now made to the diagram in FIG. 13. It is noted that thereis no significant difference among the optical properties of thepolarizing films manufactured in accordance with the examples 4 to 6. Itis understood from the results that the thickness of the PVA type resinlayer or the type of the non-crystallizable ester type thermoplasticresin does not affect the optical properties.

(4) Improvement in the Optical Properties of the Polarizing FilmProvided by the Preliminary in-Air Stretching Ratio (Examples 7 to 9)

In the example 4, the stretching ratio of the first stage preliminaryin-air stretching has been 1.8 and that of the second stagein-boric-acid-solution stretching has been 3.3, whereas in the examples7 to 9, the stretching ratios of the first stage preliminary in-airstretching and the second stage in-boric-acidsolution stretching haverespectively been 1.2 and 4.9, 1.5 and 4.0, and 2.5 and 2.4. Thepolarizing films of the examples 7 to 9 have been manufactured under thesame conditions including the stretching temperature of 130° C. and theboric acid solution temperature of 75° C. as in the example 4 except thestretching ratios. The total stretching ratio in each one of theexamples 8 and 9 has been 6.0, which is not noticeably different fromthe total stretching ratio of the example 4 wherein the total stretchingratio of 5.94 has been accomplished by the preliminary in-air stretchingwith the ratio of 1.8. However, in contrast to this, the totalstretching ratio of the example 7 has been limited to 5.88. This resulthas been caused by the fact that it has not been possible to bring thestretching ratio of the in-boric-acid-solution stretching t a levelbeyond 4.9. It is assumed that this result has been obtained due to theinfluence of the stretchable ratio of non-crystallizable PET on therelationship between the total stretching ratio and the first stagepreliminary in-air stretching ratio, as explained with reference to FIG.20.

Reference is now made to the diagram in FIG. 14. It is noted that eachof the polarizing films of the examples 7 to 9, as well as the example4, has overcome the technical objects of the present invention, and hasoptical properties satisfying the required performance that the presentinvention aims at. The optical property of the example 9 has the bestproperties among the examples, followed by the example 4, then followedby the example 8, and the example 7. It shows that when the stretchingratio of the first stage preliminary in-air stretching is in a range of1.2 to 2.5, even if the total stretching ratio after the second stagein-boric-acid-solution stretching is similar, the optical properties ofthe polarizing film are improved with an increase in the stretchingratio of the first stage preliminary in-air stretching. Thus, byincreasing the stretching ratio of the first stage preliminary in-airstretching in the manufacturing process of the optical film laminate 10including the polarizing film 3, the optical properties of themanufactured polarizing film or the optical film laminate 10 includingthe polarizing film can further be improved.

(5) Improvement of the Optical Properties of the Polarizing FilmProvided by the Preliminary in-Air Stretching Temperature (Examples 10to 12)

In the example 4, the preliminary in-air stretching temperature has beencontrolled at 130° C., whereas in the examples 10 to 12, the stretchingtemperature have respectively been controlled at 95° C., 110° C., and150° C., which are higher than the glass transition temperature Tg ofPVA. These polarizing films have been manufactured under the sameconditions including, for example, the preliminary in-air stretchingratio of 1.8 and the in-boric-acid-solution stretching ratio of 3.3 asin the example 4 except the stretching temperature.

Reference is now to be made to the diagram in FIG. 15. It is noted thateach of the polarizing films of the examples 4 and 10 to 12 has overcomethe technical problems of the present invention, and has opticalproperties satisfying the required performance that the presentinvention aims at. The optical properties of the example 12 are the mostsuperior among the examples, followed by the example 4, followed by theexample 11, and the example 10. It shows that when the stretchingtemperature of the first stage preliminary in-air stretching iscontrolled to be higher than the glass transition temperature and tosequentially increase from 95° C. to 150° C., even if the totalstretching ratio after the second stage in-boric acid solutionstretching is similar, the optical properties of the polarizing film canbe improved with increase of the stretching temperature of the firststage preliminary in-air stretching. Thus, it is to be understood thatby raising the stretching temperature of the first stage preliminaryin-air stretching in the manufacturing process of the optical filmlaminate 10 including the polarizing film 3, the optical properties ofthe manufactured polarizing film or the optical film laminate 10including the polarizing film can further be improved.

(6) Improvement of the Optical Property of the Polarizing Film Providedby the Total Stretching Ratio (Examples 13 to 15)

In the example 4, the first stage preliminary in-air stretching ratiohas been 1.8 and the second stage in-boric acid solution stretchingratio has been 3.3, whereas in the examples 13 to 15, only the secondstage in-boric acid solution stretching ratio has been changed to 2.1,3.1 and 3.6, respectively to provide the total stretching ratio for eachof the examples 13 to 15 of 5.04 (about 5.0), 5.58 (about 5.5) and 6.48(about 6.5), respectively. These polarizing films have been manufacturedunder the same conditions as in the example 4 except the totalstretching ratio.

Reference is made herein to the diagram in FIG. 16. It is noted thateach of the polarizing films of the examples 4 and 13 to 15 has overcomethe technical problems of the present invention, and has opticalproperties satisfying the required performance that the presentinvention aims at. The optical properties of the example 15 are the mostsuperior among the examples, followed by the example 4, followed by theexample 14, and the example 13. It shows that when the stretching ratioof the first stage preliminary in-air stretching is fixed at 1.8 andonly the stretching ratio in the second stage in-boric-acid solutionstretching is varied to provide the sequentially increasing totalstretching ratio of 5.0, 5.5, 6.0 and 6.5, the optical properties of thepolarizing film can be improved with increase of the total stretchingratio. Thus, by raising the total stretching ratio of the first stagepreliminary in-air stretching and the second stagein-boric-acid-solution stretching in the manufacturing process of theoptical film laminate 10 including the polarizing film 3, the opticalproperties of the manufactured polarizing film or the optical filmlaminate 10 including the polarizing film may further be improved.

(7) Improvement of the Optical Properties of the Polarizing FilmProvided by the Total Stretching Ratio in the Fixed-End UniaxialStretching (Examples 16 to 18)

In the examples 16 to 18, optical film laminates have been manufacturedunder the same conditions as in the example 4 except the stretchingprocess in the preliminary in-air stretching. In the example 4, thepreliminary in-air stretching has adopted an end-free uniaxialstretching, whereas in each of the examples 16 to 18, a fixed-enduniaxial stretching has been adopted for the preliminary in-airstretching. In the examples 16 to 18, the stretching ratio accomplishedin each case by the first stage preliminary in-air stretching has beencontrolled at 1.8 and only that of the second stagein-boric-acid-solution stretching has been varied in the respectivecases to the values 3.3, 3.9 and 4.4, respectively, to provide the totalstretching ratio of 5.94 (about 6.0) in the example 16, 7.02 (about 7.0)in the example 17, and 7.92 (about 8.0) in the example 18. Othermanufacturing conditions for the examples 16 to 18 have been the same asin the example 4.

Refer to the diagram in FIG. 17. It is noted that each of the polarizingfilms of the examples 16 to 18 has overcome the technical problems ofthe present invention, and has optical properties satisfying therequired performance that the present invention aims at. The opticalproperties of the example 18 are the most superior among the examples,followed by the example 17, and the example 16. It shows that when thestretching ratio of the first stage preliminary in-air stretching iscontrolled to be 1.8 and only the stretching ratio in the second stagein-boric acid solution stretching is varied to provide the totalstretching ratio to increase as 6.0, 7.0 and 8.0, the optical propertiesof the polarizing film can be improved with increase of the totalstretching ratio. Thus, by raising the total stretching ratio of thefirst stage fixed-end uniaxial preliminary in-air stretching and thesecond stage in-boric-acid-solution stretching in the manufacturingprocess of the optical film laminate 10 including the polarizing film 3,the optical properties of the manufactured polarizing film or theoptical film laminate 10 including the polarizing film can further beimproved. Further, it can be confirmed that the total stretching ratiocan be increased when a fixed-end uniaxial stretching is adopted for thefirst stage preliminary in-air stretching, compared with a case whereinan end-free uniaxial stretching has been adopted.

EXAMPLES

FIGS. 26 and 27 show a list of manufacturing conditions of thepolarizing films or the optical film laminates including the polarizingfilms in accordance with the examples 1 to 18.

Example 1

A continuous web of substrate has been produced from anon-crystallizable ester type thermoplastic resin comprising isophthalicacid-copolymerized polyethylene terephthalate (hereinafter referred as“non-crystallizable PET”) containing 6 mol % of isophthalic acidcopolymerized therein. The glass transition temperature of thenon-crystallizable PET is 75° C. A laminate comprising a continuous webof non-crystallizable PET substrate and polyvinyl alcohol (hereinafterreferred as “PVA”) layer has been produced in accordance with thefollowing procedures. It should be noted that the glass transitiontemperature of PVA is 80° C.

First, a non-crystallizable PET substrate 1 with a thickness of 200 μmhas been prepared together with a PVA solution having a PVAconcentration of 4 to 5 wt % which has been prepared by dissolvingpowders of PVA of a degree of polymerization of 1000 or higher and adegree of saponification of 99% or higher in water. Then, the PVAsolution has been applied to the 200 μm-thick non-crystallizable PETsubstrate in the form of a thin coating layer, and dried at atemperature of 50 to 60° C., to form a 7 μm-thick PVA layer on thenon-crystallizable PET substrate. Hereinafter, is the product formed asabove is referred as “a laminate including a 7 μm-thick PVA layer formedon a non-crystallizable PET substrate,” or “a laminate including a 7μm-thick PVA layer,” or simply as “a laminate.”

The laminate including the 7 μm-thick PVA layer has been subjected tothe following process including a 2-stage stretching comprised of apreliminary in-air stretching and an in-boric-acid-solution stretchingto produce a 3 μm-thick polarizing film. Through the first stagepreliminary in-air stretching, the laminate including the 7 μm-thick PVAlayer has been stretched together with the non-crystallizable PETsubstrate to form a stretched laminate including a 5 μm-thick PVA layer,which will hereinafter be referred as “a stretched laminate.” Describingin more detail, the stretched laminate has been produced from thelaminate including the 7 μm-thick PVA layer by subjecting it to anend-free uniaxial stretching by means of the stretching apparatusarranged in the oven maintained at a stretching temperature of 130° C.to attain a stretching ratio of 1.8. Through this stretching process,the PVA layer included in the stretched laminate has been converted intoa 5 μm-thick PVA layer having PVA molecules oriented therein.

Next, the stretched laminate has been subjected to a dyeing processwhereby iodine has been impregnated in the 5 μm-thick PVA layer whichhas PVA molecules in an oriented state to produce a laminate having adyed PVA layer, which hereinafter will be referred as “a dyed laminate.”Describing in more detail, the dyed laminate contains iodine impregnatedin the PVA layer of the stretched laminate, and is formed by immersingthe stretched laminate for an appropriate time in a dyeing solution at asolution temperature of 30° C. containing iodine and potassium iodide,to thereby convert the PVA layer into a polarizing film having a singlelayer transmittance (T) of 40 to 44%. In the process, use has been madeof a dyeing solution containing water as a solvent and iodine at aconcentration in a range of 0.12 to 0.30 wt %, and potassium iodide of0.7 to 2.1 wt %, the ratio of concentration of iodine to that ofpotassium iodide being 1:7.

It is to be noted that potassium iodide is required in order to haveiodine dissolved in water. More in detail, the stretched laminate wasimmersed for 60 seconds in the dyeing solution having iodineconcentration of 0.30 wt % and potassium iodide concentration of 2.1 wt% to form a dyed laminate having iodine impregnated in the 5 μm-thickPVA layer which includes PVA molecules in an oriented state. In theexample 1, immersion time of the stretched laminate in the dyeingsolution having iodine concentration of 0.30 wt % and potassium iodideconcentration of 2.1 wt % has been varied for controlling the amount ofiodine impregnated in the PVA layer, so that the polarizing filmconstituted by the PVA layer possesses a single layer transmittance of40 to 44%, and that variously different dyed laminates with differentsingle layer transmittance values and different polarization rates areobtained.

In the second stage of the in-boric-acid-solution stretching, the dyedlaminate has further been stretched together with the non-crystallizablePET substrate to form an optical film laminate including the PVA layerproviding a 3 μm-thick polarizing film. Hereinafter, the laminate thusformed will be referred as “an optical film laminate.” Describing inmore detail, the optical film laminate has been formed from the dyedlaminate by transporting the dyed laminate through a stretchingapparatus arranged in a processing apparatus having a bath of boric acidsolution containing boric acid and potassium iodide at a solutiontemperature of 65° C. to 85° C., was and subjecting it to an end-freeuniaxial stretching to attain a stretching ratio of 3.3. More in detail,the boric acid solution temperature has been controlled to 65° C. Theboric acid solution contained 4 parts in weight of boric acid withrespect to 100 parts in weight of water, and 5 parts in weight ofpotassium iodide with respect to 100 parts in weight of water.

In the process, the dyed laminate having the controlled amount ofimpregnated iodine has first been immersed in the boric acid solutionfor 5 to 10 seconds. The dyed laminate has then been transported in thestate it is immersed in the solution through a plurality of pairs ofrolls driven at different peripheral speeds to provide the stretchingapparatus in the processing apparatus for carrying out the end-freeuniaxial stretching to attain a stretching ratio of 3.3 in 30 to 90seconds. Through this stretching, the PVA layer included in the dyedlaminate is converted into a 3 μm-thick PVA layer having iodineimpregnated therein with a high-order orientation in one direction inthe form of a polyiodide ion complex. The PVA layer provides thepolarizing film in the optical film laminate.

As described above, in the example 1, the laminate including the 7μm-thick PVA layer formed on the non-crystallizable PET substrate hasfirst been subjected to a preliminarily in-air stretching at astretching temperature of 130° C. to form the stretched laminate, thenthe stretched laminate has been dyed to form the dyed laminate, the dyedlaminate having been subjected to an in-boric-acid-solution stretchingat a stretching temperature of 65° C., to attain the total stretchingratio of 5.94, to thereby form the optical film laminate including the 3μm-thick PVA layer which has been stretched together with thenon-crystallizable PET substrate. Through such 2-stage stretching, ithas become possible to attain a high-order orientation of the PVAmolecules in the PVA layer formed on the non-crystallizable PETsubstrate to form the optical film laminate including the 3 μm-thick PVAlayer which finally constitutes the polarizing film having iodineimpregnated therein through the dyeing process with a high-orderorientation in the form of a polyiodide ion complex.

Although not an essential process for manufacturing an optical filmlaminate, the optical film has been taken out of the boric acidsolution, and then cleaned with potassium iodide solution to remove anyboric acid deposited on the surface of the 3 μm-thick PVA layer formedon the non-crystallizable PET substrate. Subsequently, the cleanedoptical film laminate has been dried with warm air at a temperature of60° C. in a drying process. The cleaning process aims at improvingappearance by washing out boric acid deposition.

Although similarly not an essential process for manufacturing an opticalfilm laminate, in laminating/transferring process, bonding agent wasapplied on the surface of the 3 μm-thick PVA layer formed on thenon-crystallizable PET substrate and an 80 μm-thick triacetylcellulose(TAC) film has been attached thereto through the bonding agent, andthereafter the non-crystallizable PET substrate has been peeled to havethe 3 μm-thick PVA layer transferred to the 80 μm-thicktriacetylcellulose (TAC) film.

Example 2

In the example 2, as in the example 1, a laminate has at first providedby forming a 7 μm-thick PVA layer on a non-crystallizable PET substrate,then the laminate including the 7 μm-thick PVA layer has been subjectedto a preliminary in-air stretching, to a stretching ratio of 1.8 tothereby form a stretched laminate, and thereafter the stretched laminatehas been immersed in a dyeing solution containing iodine and potassiumiodide at a solution temperature of 30° C. to form a dyed laminateincluding a PVA layer having iodine impregnated therein. In the example2, in contrast to the example 1, a cross-linking process hasadditionally been carried out by immersing the dyed laminate for 60seconds in the boric acid cross-linking solution at a solutiontemperature of 40° C. for the purpose of cross-linking PVA molecules inthe PVA layer having iodine impregnated therein. The boric acidcross-linking solution in this process has contained 3 parts in weightof boric acid with respect to 100 parts in weight of water and 3 partsin weight of potassium iodide with respect to 100 parts in weight ofwater.

The cross-linking process in the example 2 is considered to provide atleast 3 technical effects. The first is an insolubilization forpreventing the reduced thickness PVA layer in the dyed laminate frombeing dissolved during the following in-boric-acid-solution stretching.The second is the dye stabilization for preventing the iodineimpregnated in the PVA layer from being eluted. The third is thefunction of forming junction points by cross-linking the molecules inthe PVA layer.

The method in the example 2 has further included a process in which thecross-linked dyed laminate has then been immersed in the stretching poolcontaining an in-boric acid solution at a solution temperature of 75°C., which is higher than the stretching temperature of 65° C. in theexample 1, to stretch the laminate to a stretching ratio of 3.3 as inthe example 1, to thereby form an optical film laminate. It shouldfurther be noted that, each of cleaning, drying andlaminating/transferring process in the example 2 had been the same asthat in the example 1.

To clarify the technical meritorious effect attained by thecross-linking process which has been conducted prior to thein-boric-acid-solution stretching, the non-cross-linked dyed laminate inthe example 1 has been immersed in the in-boric-acid-solution stretchingpool at a solution temperature of 70 to 75° C., to find that the PVAlayer included in the dyed laminate dissolved in the solution in thestretching pool so that the stretching process has not been able to becarried out.

Example 3

In the example 3, as in the example 1, a laminate has first beenprepared by forming a 7 μm-thick PVA layer on a non-crystallizable PETsubstrate, then the laminate including the 7 μm-thick PVA layer has beensubjected to a preliminary in-air stretching to attain a stretchingratio of 1.8, to thereby form a stretched laminate. In the example 3, incontrast to the example 1, an insolubilizing process has beenadditionally incorporated, for insolubilizing the PVA layer in thestretched laminate and having PVA molecules oriented, the insolubilizingprocess being carried out by immersing the stretched laminate for 30seconds in boric acid insolubilizing solution at a solution temperatureof 30° C. The boric acid insolubilizing solution in this process hascontained 3 parts in weight of boric acid with respect to 100 parts inweight of water. The technical effect obtained by the insolubilizationprocess in the example 3 is that the PVA layer in the stretched laminateis insolubilized so that it will not be eluted at least during thefollowing dyeing process.

In the example 3, the insolubilized and stretched laminate has then beenimmersed, as in the example 1, in a dyeing solution containing iodineand potassium iodide at a solution temperature of 30° C. to form a dyedlaminate including a PVA layer having iodine impregnated therein.Subsequently, the dyed laminate has been immersed in the in-boric acidsolution stretching pool at a solution temperature of 65° C., which issame as the stretching temperature in the example 1, to stretch thelaminate to a stretching ratio of 3.3 as in the example 1, to therebyform an optical film laminate. It is further to be noted that each ofthe cleaning, drying and laminating/transferring processes in theexample 3 has been the same as that in the example 1.

To clarify the technical meritorious effect attained by theinsolubilizing process which is carried out prior to the dyeing process,the non-insolubilized stretched laminate in the example 1 has been dyedto form a dyed laminate, then the dyed laminate has been immersed in thein-boric-acid-solution stretching pool at a solution temperature of 65to 75° C., to find that the PVA layer in the dyed laminate dissolved inthe solution of the stretching pool so that the laminate has not beenstretchable.

When the non-insolubilized stretched laminate in the example 1 has beenimmersed in a dyeing solution containing water as solvent and iodine ata concentration of 0.12 to 0.25 wt %, instead of iodine at aconcentration of 0.30 wt % in the example 1, but other conditions beingmaintained unchanged, the PVA layer included in the stretched laminatehas dissolved in the dying pool so that the laminated cannot be dyed.However, when the insolubilized stretched laminate in the example 3 hasbeen used, the PVA layer has not been dissolved even at the iodineconcentration in the range of 0.12 to 0.25 wt % so that the dyeingprocess has been carried out.

In the example 3 wherein the PVA layer can be dyed successfully evenwith iodine concentration of 0.12 to 0.25 wt % in the dyeing solution,variety of different dyed laminates have been produced with a constantimmersion time of the stretched laminate in the dyeing solution and withdifferent iodine concentrations and different potassium iodideconcentrations in the dyeing solution in the range described withrespect to the example 1, by controlling the amount of the impregnatediodine so that the polarizing films provided by the PVA layers in thefinal products have different values of single transmittance anddifferent polarization rates, with the values of the single layertransmittance in the range of 40 to 44%.

Example 4

In the example 4, an optical film laminate has been produced through amanufacturing process where insolubilizing process in the example 3 andcross-linking process in the example 2 have additionally incorporated inthe manufacturing process in the example 1. Firstly, a laminate has beenprovided by forming a 7 μm-thick PVA layer on a non-crystallizable PETsubstrate, then, the laminate including the 7 μm-thick PVA layer hasbeen subjected to an end-free uniaxial in-air stretching to attain astretching ratio of 1.8, to thereby form a stretched laminate. In theexample 4, as in the example 3, the formed stretched laminate has beenimmersed in a boric acid insolubilizing solution at a solutiontemperature of 30° C. for 30 seconds to have the PVA layer in thestretched laminate insolubilized with PVA molecules in an orientedstate. In the example 4, the stretched laminate comprising theinsolubilized PVA layer has further been immersed, as in the example 3,in a dyeing solution containing iodine and potassium iodide at asolution temperature of 30° C. to form a dyed laminate including a PVAlayer having iodine impregnated therein.

In the example 4, as in the example 2, the dyed laminate thus formed hasbeen immersed in a boric acid cross-linking solution at a solutiontemperature of 40° C. for 60 seconds to have the PVA moleculescross-linked in the PVA layer in which iodine is impregnated. In theexample 4, the dyed laminate including the cross-linked PVA layer hasfurther been immersed for 5 to 10 seconds in an in-boric acid solutionstretching pool at a solution temperature of 75° C., which is higherthan the stretching temperature of 65° C. in the example 1, to subjectthe laminate to an end-free uniaxial stretching to attain a stretchingratio of 3.3 as in the example 2, to thereby form an optical filmlaminate. Each of the cleaning, drying and laminating/transferringprocesses in the example 4 has been the same as that in the examples 1to 3.

In the example 4, as in the example 3, the PVA layer has not beendissolved even at the iodine concentration in the range of 0.12 to 0.25wt %. In the example 4, various dyed laminates have been produced with aconstant immersion time of the stretched laminate in the dyeing solutionand with various iodine concentrations and potassium iodideconcentrations in the dyeing solution in the range described withrespect to the example 1, by controlling the amount of the impregnatediodine so that the polarizing films provided by the PVA layers haverespectively different values of single layer transmittance anddifferent polarization rates with the range of single layer being in therange of 40 to 44%.

As above, in the example 4, a laminate has first been produced byforming a 7 μm-thick PVA layer on a non-crystallizable PET substrate,then, subjecting the laminate including the 7 μm-thick PVA layer to anend-free uniaxial stretching in a preliminary in-air stretching process,to attain a stretching ratio of 1.8, to thereby form a stretchedlaminate. The stretched laminate thus formed has been immersed in aboric acid insolubilizing solution at a solution temperature of 30° C.for 30 seconds to have the PVA layer included in the stretched laminateinsolubilized with PVA molecules in an oriented state. The stretchedlaminate including the insolubilized PVA layer has further been immersedin a dyeing solution containing iodine and potassium iodide at asolution temperature of 30° C. to form a dyed laminate including a PVAlayer having iodine impregnated therein. The dyed laminate has beenimmersed in boric acid cross-linking solution at a solution temperatureof 40° C. for 60 seconds to have PVA molecules cross-linked in the PVAlayer having iodine impregnated therein. The dyed laminate including thecross-linked PVA layer has further been immersed for 5 to 10 seconds inan in-boric acid solution stretching pool containing iodine andpotassium iodide at a solution temperature of 75° C., then has beenprocessed in an end-free uniaxial stretching to attain a stretchingratio of 3.3, to thereby form an optical film laminate.

In the example 4, because of the 2-stage stretching process consistingof an elevated temperature in-air stretching and anin-boric-acid-solution stretching together with the pre-processingconsisting of an insolubilizing process prior to immersion in dyeingpool and a cross-linking process prior to the in-boric-acid-solutionstretching, it has become possible to manufacture in a stable manner anoptical film laminate including a 3 μm-thick PVA layer having iodineimpregnated therein through a dyeing process and providing a polarizingfilm having PVA molecules oriented with a high-order orientation in onedirection in the form of a polyiodide ion complex in the PVA layerformed on the non-crystallizable PET substrate.

Example 5

In the example 5, an optical film laminate has been manufactured underthe same conditions as in the example 4 except the thickness of the PVAlayer formed on the non-crystallizable PET substrate. In the example 4,the thickness of the PVA layer has been 7 μm before stretching, and thatof the PVA layer in the finally manufactured optical film laminate hasbeen 3 μm, whereas in the example 5, the thickness of the PVA layerbefore stretching has been 12 μm, and that of the PVA layer in thefinally manufactured optical film laminate has been 5 μm.

Example 6

In the example 6, an optical film laminate has been manufactured underthe same conditions as in the example 4 except the polymerizing monomerin the non-crystallizable PET substrate. In the example 4, use has beenmade of a non-crystallizable PET substrate having isophthalic acidcopolymerized in the PET, whereas in the example 6, a non-crystallizablePET substrate has had 1,4-cyclohexanedimethanol copolymerized in the PETas a modifier group.

Example 7

In the example 7, an optical film laminate has been manufactured underthe same conditions as in the example 4 except that the stretching ratiofor each of the preliminary in-air stretching and thein-boric-acid-solution stretching has been varied so that the totalstretching ratio became 6.0 or a value close to 6.0. In the example 4,the stretching ratios for the preliminary in-air stretching and thein-boric acid solution stretching have respectively been 1.8 and 3.3,whereas in the example 7, the respective ones of the ratios have been1.2 and 4.9. The reason for the difference of the total stretching ratioin the example 4 of 5.94 and that in the example 7 of 5.88 is that ithas not been possible to raise the in-boric-acid-solution stretchingratio above 4.9 in the example 7.

Example 8

In the example 8, an optical film laminate has been manufactured underthe same conditions as in the example 4 except the stretching ratio foreach of the preliminary in-air stretching and the in-boric acid solutionstretching was varied so that the total stretching ratio has become 6.0.In the example 8, the stretching ratios for the preliminary in-airstretching and the in-boric-acid-solution stretching have been 1.5 and4.0, respectively.

Example 9

In the example 9, an optical film laminate has been manufactured underthe same conditions as in the example 4 except that different valueshave been adopted for the stretching ratio for each of the preliminaryin-air stretching and the in-boric acid solution stretching to attainthe total stretching ratio of 6.0. In the example 9, the stretchingratios for the preliminary in-air stretching and the in-boric acidsolution stretching have been 2.5 and 2.4, respectively.

Example 10

In the example 10, an optical film laminate has been manufactured underthe same conditions as in the example 4 except a difference in thestretching temperature. In the example 10, the stretching temperaturefor the preliminary in-air stretching has been 95° C., whereas in theexample 4, the corresponding temperature has been 130° C.

Example 11

In the example 11, an optical film laminate has been manufactured underthe same conditions as in the example 4 except a difference in thestretching temperature. In the example 11, the stretching temperaturefor the preliminary in-air stretching has been 110° C., whereas in theexample 4, the corresponding temperature has been 130° C.

Example 12

In the example 12, an optical film laminate has been manufactured underthe same conditions as in the example 4 except a difference in thestretching temperature. In the example 12, the stretching temperaturefor the preliminary in-air stretching has been 150° C., whereas in theexample 4, the corresponding temperature has been 130° C.

Example 13

In the example 13, an optical film laminate has been manufactured underthe same conditions as in the example 4 except that a different valuehas been adopted as the stretching ratio for the in-boric-acid-solutionstretching. In the example 13, the stretching ratio for the preliminaryin-air stretching and that for the in-boric-acid-solution stretchinghave been 1.8 and 2.8, respectively, whereas in the example 4, thecorresponding values have been 1.8 and 3.3, respectively. In the example13, the total stretching ratio has therefore been about 5.0 (5.04 to beaccurate), whereas in the example 4, the corresponding ratio has beenabout 6.0 (5.94 to be accurate).

Example 14

In the example 14, an optical film laminate has been manufactured underthe same conditions as in the example 4 except that a different valuehas been adopted as the stretching ratio for the in-boric acid solutionstretching. In the example 14, the stretching ratio for the preliminaryin-air stretching and that for the in-boric acid solution stretchinghave been 1.8 and 3.1, respectively, whereas in the example 4, thecorresponding values have been 1.8 and 3.3, respectively. In the example14, the total stretching ratio has therefore become about 5.5 (5.58 tobe accurate), whereas in the example 4, it has been about 6.0 (5.94 tobe accurate).

Example 15

In the example 15, an optical film laminate has been manufactured underthe same conditions as in the example 4 except that a different valuehas been adopted as the stretching ratio for the in-boric acid solutionstretching. In the example 15, the stretching ratio for the preliminaryin-air stretching and that for the in-boric-acid-solution stretchinghave been 1.8 and 3.6, respectively, whereas in the example 15, thecorresponding values have been 1.8 and 3.3, respectively. In the example15, the total stretching ratio has therefore become about 6.5 (6.48 tobe accurate), whereas in the example 4, the corresponding value has beenabout 6.0 (5.94 to be accurate).

Example 16

In the example 16, an optical film laminate has been manufactured underthe same conditions as in the example 4 except the stretching processfor the preliminary in-air stretching. In the example 16, the laminatehas been subjected to a fixed-end uniaxial stretching in the preliminaryin-air stretching to attain the stretching ratio of 1.8, whereas in theexample 4, an end-free uniaxial stretching has been adopted in thepreliminary in-air stretching to attain the stretching ratio of 1.8.

Example 17

In the example 17, an optical film laminate has been manufactured underthe same conditions as in the example 16 except that a different valuehas been adopted as the stretching ratio for the in-boric acid solutionstretching. In the example 17, the stretching ratio for the preliminaryin-air stretching and that for the in-boric acid solution stretchinghave been 1.8 and 3.9, respectively, whereas in the example 16, thecorresponding values have been 1.8 and 3.3, respectively. In the example17, the total stretching ratio has therefore become about 7.0 (7.02 tobe accurate), whereas in the example 16, the corresponding value hasbeen about 6.0 (5.94 to be accurate).

Example 18

In the example 18, an optical film laminate has been manufactured underthe same conditions as in the example 16 except that a different valuehas been adopted as the stretching ratio for the in-boric acid solutionstretching. In the example 18, the stretching ratio for the preliminaryin-air stretching and that for the in-boric-acid-solution stretchinghave been 1.8 and 4.4, respectively, whereas in the example 16, thecorresponding values have been 1.8 and 3.3, respectively. In the example18, the total stretching ratio has therefore become about 8.0 (7.92 tobe accurate), whereas in the example 16, the corresponding value hasbeen about 6.0 (5.94 to be accurate).

(Comparative Test Sample 1)

In the comparative test sample 1, a laminate has been manufactured underthe same conditions as in the example 4. First, a laminate has beenproduced by forming a 7 μm-thick PVA layer on a non-crystallizable PETsubstrate by applying PVA solution on a 200 μm-thick non-crystallizablePET substrate and drying the same. Then, the laminate including the 7μm-thick PVA layer has been subjected to an end-free uniaxial stretchingin an elevated temperature in-air stretching process at a stretchingtemperature of 130° C. to attain a stretching ratio became 4.0 tothereby form a stretched laminate. After the stretching, the PVA layerincluded in the stretched laminate has been reduced in thickness toproduce a 3.5 μm-thick PVA layer which has PVA molecules orientedtherein.

Then, the stretched laminate has been dyed to form a dyed laminatehaving iodine impregnated in the 3.5 μm-thick PVA layer including PVAmolecules oriented therein. Describing more specifically, the dyedlaminate has been formed by immersing the stretched laminate in a dyeingsolution containing iodine and potassium iodide at a solutiontemperature of 30° C. for an appropriate time to have iodine impregnatedtherein so that a polarizing film formed by the PVA layer has a singlelayer transmittance of 40 to 44%. The amount of impregnated iodine hasbeen controlled to produce variously different dyed laminates withdifferent values of the single layer transmittance and those of thepolarization rate.

Further, the dyed laminated has been subjected to a cross-linkingprocess, particularly, by immersing the dyed laminate in a boric acidcross-linking solution containing 3 parts in weight of boric acid withrespect to 100 parts in weight of water and 3 parts in weight ofpotassium iodide with respect to 100 parts in weight of water at asolution temperature of 40° C. for 60 seconds. The cross-linked dyedlaminate in the comparative test sample 1 corresponds to the opticalfilm laminate in accordance with the example 4. Thus, the cleaning,drying and laminating and/or transferring processes in the comparativetest sample 1 have been similar to those in the example 4.

(Comparative Test Sample 2)

In the comparative test sample 2, the stretched laminates provided inthe comparative test sample 1 have been stretched under the sameconditions to attain the stretching ratio of 4.5, 5.0 and 6.0,respectively. The above comparative table sets forth various propertiesobtained in the 200 μm-thick non-crystallizable PET substrate and thePVA layer formed on the non-crystallizable PET substrate, including thecomparative test samples 1 and 2. It is thereby confirmed that thestretching ratio of the elevated temperature in-air stretching at thestretching temperature of 130° C. has an upper limit at the value 4.0.

(Comparative Test Sample 3)

In the comparative test sample 3, under the same conditions as in thecomparative test sample 1, a laminate has been produced by forming a 7μm-thick PVA layer on a non-crystallizable PET substrate by applying PVAsolution on a 200 μm-thick non-crystallizable PET substrate and dryingthe same. Then, the laminate comprising the 7 μm-thick PVA layer hasbeen immersed in a dyeing solution containing iodine and potassiumiodide at a solution temperature of 30° C. to form a dyed laminateincluding a PVA layer having iodine impregnated therein. Describing inmore detail, the dyed laminate has been formed by immersing thestretched laminate in a dyeing solution containing 0.30 wt % of iodineand 2.1 wt % of potassium iodide at a solution temperature of 30° C. foran appropriate time so that a polarizing film provided by the PVA layerpossesses a single layer transmittance of 40 to 44%. Then, the dyedlaminate including the PVA layer having iodine impregnated therein hasbeen subjected to an end-free uniaxial stretching in a boric acidsolution at a stretching temperature of 60° C. to attain a stretchingratio of 5.0. Thus, there have been produced through different immersiontime periods various optical laminates each including such 3 μm-thickPVA layer integrally stretched with the PET resin substrate.

(Reference Test Sample 1)

In the reference test sample 1, a laminate has been produced by forminga 7 μm-thick PVA layer on a crystallizable PET substrate by using acontinuous web of crystallizable polyethylene terephthalate (hereinafterreferred as crystallizable PET) as resin substrate and by applying PVAsolution on a 200 μm-thick crystallizable PET substrate and drying thesame. Glass transition temperature of the crystallizable PET is 80° C.Then, the formed laminate has been subjected to an end-free uniaxialstretching in an elevated temperature in-air stretching process at astretching temperature of 110° C. to attain a stretching ratio of 4.0 tothereby form a stretched laminate. Through the stretching, the PVA layerin the stretched laminate has been converted into a 3 μm-thick PVA layerhaving PVA molecules oriented therein. In the reference test sample 1,it has not been possible to stretch the laminate to a stretching ratiobeyond 4.0 in the elevated temperature in-air stretching at a stretchingtemperature of 110° C.

The stretched laminate has then been dyed to form a dyed laminate whichincludes iodine impregnated in the 3.5 μm-thick PVA layer which has PVAmolecules in an oriented state. Describing more specifically, the dyedlaminate has been formed by immersing the stretched laminate in a dyeingsolution containing iodine and potassium iodide at a solutiontemperature of 30° C. for an appropriate time to have iodine impregnatedtherein so that the polarizing film provided by the PVA layer possessesa single layer transmittance of 40 to 44%. The amount of impregnatediodine has been changed to produce variously different dyed laminateshaving different values of single layer transmittance and those ofpolarization rate. Then, the dyed laminated has been subjected to across-linking process, particularly, by immersing the dyed laminate in aboric acid cross-linking solution containing 3 parts in weight of boricacid with respect to 100 parts in weight of water and 3 parts in weightof potassium iodide with respect to 100 parts in weight of water at asolution temperature of 40° C. for 60 seconds. The cross-linked dyedlaminate in the comparative test sample 1 corresponds to the opticalfilm laminate in accordance with the example 4. Thus, the cleaning,drying and laminating and/or transferring processes in the comparativetest sample 1 have been similar to those in the example 4.

(Reference Test Sample 2)

In the reference test sample 2, a laminate has been produced by forminga 7 μm-thick PVA layer on a 200 μm-thick crystallizable PET substrate asin the reference test sample 1. Then, the formed laminate has beensubjected to an end-free uniaxial stretching through an elevatedtemperature in-air stretching process at a stretching temperature of100° C. to attain a stretching ratio of 4.5 to thereby form a stretchedlaminate. Through the stretching process, the PVA layer has beenconverted in the stretched laminate into a 3.3 μm-thick PVA layer havingPVA molecules oriented therein. In the reference test sample 2, it hasnot been possible to stretch the laminate beyond the stretching ratio of4.5 in the elevated temperature in-air stretching under a stretchingtemperature of 100° C.

Then, a dyed laminate has been formed by immersing the stretchedlaminate in a dyeing solution containing iodine and potassium iodide ata solution temperature of 30° C. for an appropriate time to have iodineimpregnated therein so that the polarizing film provided by the PVAlayer possesses a single layer transmittance of 40 to 44%. In thereference test sample 2, the amount of iodine impregnated in the PVAlayer has been controlled as in the reference test sample 1 to formvarious different dyed laminates having different values of the singlelayer transmittance and those of polarization rate.

(Reference Test Sample 3)

In the reference test sample 3, as in the reference test samples 1 and2, a laminate has been produced by forming a 7 μm-thick PVA layer on acrystallizable PET substrate by applying PVA solution on a 200 μm-thickcrystallizable PET substrate. Then, the formed laminate has beenimmersed in a dyeing solution containing iodine and potassium iodide ata solution temperature of 30° C. for an appropriate time to have iodineimpregnated therein so that the polarizing film provided by the PVAlayer possesses a single layer transmittance of 40 to 44% and variousdifferent dyed laminates have been produced with different immersiontime. Subsequently, thus formed dyed laminates have been subjected to anend-free uniaxial stretching through an elevated temperature in-airstretching process at a stretching temperature of 90° C. to a stretchingratio of 4.5 to thereby form a stretched laminate including the PVAlayer having iodine impregnated therein in such an amount that the PVAlayer provides a polarizing film. Through the stretching procedure, thePVA layer having iodine impregnated therein has been converted in thestretched laminate formed from the dyed laminate, to a 3.3 μm-thick PVAlayer having PVA molecules impregnated therein. In the reference testsample 3, it has not been possible to stretch the laminate beyond thestretching ratio of 4.5 in the elevated temperature in-air stretching ata stretching temperature of 90° C.

(Measurement Process)

(Thickness Measurement)

Thickness of each of the non-crystallizable PET substrate, thecrystallizable PET substrate and the PVA layer has been measured using adigital micrometer (KC-351C from Anritsu Electric Co., Ltd.).

(Measurement of Transmittance and Polarization Rate)

Each of the single layer transmittance T, the parallel transmittance Tpand the cross transmittance Tc of the polarizing film has been measuredusing a UV-visible spectrophotometer (V7100 from JASCO Corporation). Thevalues of T, Tp and Tc are presented in terms of Y values measuredaccording to JIS Z8701 (visual field of 2 degrees, C light source) andcorrected for spectral luminous efficacy.

The polarization rate P has been calculated in accordance with thefollowing equation using the above value of transmittance.polarization rate P={(Tp−Tc)/(Tp+Tc)}×100(Evaluation of Orientation Function of PVA)

A Fourier Transform Infrared Spectrometer (FT-IR) (SPECTRUM 2000 fromPerkinElmer, Inc.) has been used as the measurement device. Attenuatedtotal reflection (ATR) of polarizing light has been measured to evaluatethe surface of the vinyl alcohol resin layer. Orientation function hasbeen calculated according to the following procedures. Measurements havebeen made on the polarizing light in the directions of 0° and 90° withrespect to the stretching direction. Intensity of the obtained spectralat 2941 cm⁻¹ has been used to calculate the orientation functionaccording to the Equation 4 (the Non-Patent Document 1) shown above. Forthe intensity I, with a value at 3330 cm⁻¹ taken as a reference peak, avalue of 2941 cm⁻¹/3330 cm⁻¹ has been used. The condition of f=1indicates the complete or perfect orientation, whereas the condition f=0indicates a random orientation. The peak observed at 2941 cm⁻¹ isconsidered as indicating the absorption induced by vibration of the mainchain of PVA (—CH2-).f=(3<cos² θ>−1)/2=[(R−1)(R ₀+2)]/[(R+2)(R ₀−1)]=(1−D)/[c(2D+1)]=−2×(1−D)/(2D+1)  (Equation 4)

where,

c=(3 cos² β−1)/2,

β=90°, an angle of transition dipole moment with respect to an axis ofmolecular chain,

θ: an angle of molecular chain with respect to stretching direction,

R₀=2 cot²β,

1/R=D=(I⊥)/(I//)(the more the PET is oriented, the greater the value ofD),

I⊥=intensity measured when polarizing light incidents perpendicular tostretching direction,

I//=intensity measured when polarizing light incidents parallel tostretching direction.

(Evaluation of Degree of Crystallization of PVA)

A Fourier Transform Infrared Spectrometer (FT-IR) (SPECTRUM 2000 fromPerkinElmer, Inc.) has been used as the measurement device. Attenuatedtotal reflection (ATR) of polarizing light has been measured to evaluatethe surface of the vinyl alcohol resin layer. Degree of crystallizationhas been calculated according to the following procedures. Measurementshave been made on the polarizing light in the directions of 0° and 90°with respect to the stretching direction. Intensities of the obtainedspectral at 1141 cm⁻¹ and at 1440 cm⁻¹ have been used to calculate thedegree of crystallization. Calculations have been made using theintensity at 1141 cm⁻¹ as relative to the amount of crystallized part,and the value at 1440 cm⁻¹ as a reference peak to determine acrystallization index with the following equation (Equation 6). Further,a sample of PVA with a known degree of crystallization has been used inadvance to create crystallization index and a calibration curve, and thecalibration curve has been used to calculate the degree ofcrystallization from the crystallization index (Equation 5).Degree of crystallization=63.8×crystallization index−44.8  (Equation 5)Crystallization index=((I(1141 cm⁻¹)0°+2+I(1141 cm⁻¹)90°)/3)/(I(1440cm⁻¹)0°+2×I(1440 cm⁻¹)90°)/3)  (Equation 6)

where,

I(1141 cm⁻¹) 0°=intensity at 1141 cm⁻¹ when polarizing light incidentsparallel to stretching direction,

I(1141 cm⁻¹) 90°=intensity at 1141 cm⁻¹ when polarizing light incidentsperpendicular to stretching direction,

I(1440 cm⁻¹) 0°=intensity at 1440 cm⁻¹ when polarizing light incidentsparallel to stretching direction,

I(1440 cm⁻¹) 90°=intensity at 1440 cm⁻¹ when polarizing light incidentsperpendicular to stretching direction.

EXPLANATION OF NUMERICAL SYMBOLS

-   1: Non-crystallizable PET substrate-   2: PVA type resin layer-   3: Polarizing film-   4: Optically functional film-   5: Second optically functional film-   7: Laminate comprising PVA type resin layer-   8: Stretched laminate-   8′: Roll of stretched laminate-   8″: Insolubilized stretched laminate-   9: Dyed laminate-   9′: Cross-linked dyed laminate-   10: Optical film laminate-   11: Optically functional film laminate-   12: Optical film laminate (pattern 1)-   13: Optical film laminate (pattern 2)-   14: Optically functional film laminate (pattern 3)-   15: Optically functional film laminate (pattern 4)-   16: Adhesive agent (Adhesive agent layer)-   17: Separator-   18: Bonding agent (Bonding agent layer)-   20: Laminate manufacturing apparatus-   21: Coating unit-   22: Drying unit-   23: Surface modifying apparatus-   30: Preliminary in-air stretching apparatus-   31: Stretching unit-   32: Winding apparatus-   33: Oven-   40: Dying apparatus-   41: Dying solution-   42: Dying pool-   43: Feeding apparatus-   50: In-boric acid solution stretching apparatus-   51: Boric acid solution-   52: Boric acid solution pool-   53: Stretching unit-   60: Insolubilizing apparatus-   61: Boric acid insolubilizing solution-   70: Cross-linking apparatus-   71: Boric acid cross-linking solution-   80: Cleaning apparatus-   81: Cleaning solution-   90: Drying apparatus-   91: Winding apparatus-   100: Laminating/transferring apparatus-   101: Feeding/laminating apparatus-   102: Winding/transferring apparatus-   200: Display panel for IPS-type liquid-crystal television-   201: Surface treatment layer-   202: IPS liquid crystal cell-   300: Display panel for VA-type liquid-crystal television-   301: Biaxial phase difference film (nx>ny>nz)-   302: VA liquid-crystal cell-   400: Display panel for IPS-type liquid-crystal television-   401: Triacetylcellulose (TAC) film-   402: IPS liquid-crystal cell-   500: Display panel for IPS-type liquid-crystal television-   501: Biaxial phase difference film (nx>nz>ny)-   502: IPS liquid-crystal cell-   600: Organic electroluminescence display panel-   601: Acrylic resin film-   602: λ/4 phase difference film-   603: Organic electroluminescence panel-   (A): Laminate manufacturing process-   (B): Preliminary in-air stretching process-   (C): Dying process-   (D): In-boric acid solution stretching process-   (E): First insolubilization process-   (F): Cross-linking process including second insolubilization-   (G): Cleaning process-   (H): Drying process-   (I): Laminating/transferring process

The invention claimed is:
 1. A method for manufacturing an optical filmlaminate including a polarizing film comprising polyvinyl alcohol typeresin formed on a non-crystallizable ester type thermoplastic resinsubstrate in the form of a continuous web and having a dichroic materialimpregnated therein in an oriented state, the method comprising stepsof: subjecting a laminate comprising the non-crystallizable ester typethermoplastic resin substrate and the polyvinyl alcohol type resin layerformed on the non-crystallizable ester type thermoplastic resinsubstrate to an elevated temperature in-air stretching to form astretched laminate including a stretched intermediate consisting of amolecularly oriented polyvinyl alcohol type resin by; impregnating thedichroic material in the stretched laminate to form a dyed laminateincluding a dyed intermediate comprising the polyvinyl alcohol typeresin layer having the dichroic material impregnated therein in anoriented state; and stretching the dyed laminate in a boric acidsolution to form the optical film laminate including the polarizing filmincluding the polyvinyl alcohol type resin having the dichroic materialimpregnated therein in an oriented state.
 2. A method for manufacturingan optical film laminate as defined by claim 1, wherein the polarizingfilm has optical property values in a range represented by:P>−(10^(0.929T-42.4)−1)×100 (where T<42.3); andP≧99.9 (where T≧42.3) where: T is a single layer transmittance and P apolarization rate.
 3. A method for manufacturing an optical filmlaminate as defined by claim 1, wherein the polarizing film has athickness of 10 μm or less.
 4. A method for manufacturing an opticalfilm laminate as defined by claim 1, wherein the non-crystallizableester type thermoplastic resin substrate has a thickness which is atleast 6 times as large as that of the polyvinyl alcohol type resin layerformed thereon.
 5. A method for manufacturing an optical film laminateas defined by claim 1, wherein the non-crystallizable ester typethermoplastic resin substrate is selected from the group includingpolyethylene terephthalate copolymerized with isophthalic acid,polyethylene terephthalate copolymerized with cyclohexanedimethanol, andnon-crystallizable polyethylene terephthalate including othercopolymerized polyethylene terephthalate.
 6. A method for manufacturingan optical film laminate as defined by claim 1, wherein thenon-crystallizable ester type thermoplastic resin substrate comprises atransparent resin.
 7. A method for manufacturing an optical filmlaminate as defined by claim 1, further comprising a step of forming thepolyvinyl alcohol type resin layer on the non-crystallizable ester typethermoplastic resin substrate by coating and drying the polyvinylalcohol type resin on the non-crystallizable ester type thermoplasticresin substrate.
 8. A method for manufacturing an optical film laminateas defined by claim 1, wherein the stretching ratio of the elevatedtemperature in-air stretching is 3.5 or less.
 9. A method formanufacturing an optical film laminate as defined by claim 1, whereinstretching temperature of the elevated temperature in-air stretching ishigher than the glass transition temperature of the polyvinyl alcoholtype resin.
 10. A method for manufacturing an optical film laminate asdefined by claim 1, wherein the stretching temperature of the elevatedtemperature in-air stretching is 95° C. to 150° C.
 11. A method formanufacturing an optical film laminate as defined by claim 1, whereinthe dyed laminate is formed by immersing the stretched laminate in adyeing solution comprised of the dichroic material.
 12. A method formanufacturing an optical film laminate as defined by claim 1, furtherincluding a first insolubilization step for having the stretchedintermediate included in the stretched laminate insolubilized beforeimmersing the stretched laminate in the dyeing solution including thedichroic material.
 13. A method for manufacturing an optical filmlaminate as defined by claim 12, wherein the first insolubilization stepincludes immersing the stretched laminate in a boric acid solutionhaving a solution temperature of no more than 40° C.
 14. A method formanufacturing an optical film laminate as defined by claim 1, whereinthe dyed laminate is stretched in the boric acid solution to form thepolarizing film having a thickness of 10 μm or less.
 15. A method formanufacturing an optical film laminate as defined by claim 1, furtherincluding a second insolubilization step for subjecting the dyedlaminate to an insolubilization treatment before stretching the dyedlaminate in the boric acid solution.
 16. A method for manufacturing anoptical film laminate as defined by claim 15, wherein the secondinsolubilization step includes immersing the dyed laminate in the boricacid solution having a solution temperature of no more than 40° C.
 17. Amethod for manufacturing an optical film laminate as defined by claim 1,wherein the stretched laminate and the dyed laminate are subjected tothe elevated temperature in-air stretching and thein-boric-acid-solution stretching to attain a total stretching ratio of5.0 or higher.
 18. A method for manufacturing an optical film laminateas defined by claim 1, wherein the solution temperature of the boricacid solution for the in-boric-acid-solution stretching is 60° C. orhigher.
 19. A method for manufacturing an optical film laminate asdefined by claim 1, wherein the elevated temperature in-air stretchingis performed under an end-free uniaxial stretching process to attain thetotal stretching ratio of 5.0 to 7.5 in the stretched laminate and thedyed laminate.
 20. A method for manufacturing an optical film laminateas defined by claim 1, wherein the elevated temperature in-airstretching is performed under an end-fixed uniaxial stretching processto attain the total stretching ratio of 5.0 to 8.5 in the stretchedlaminate and the dyed laminate.
 21. A method for manufacturing anoptical film laminate as defined by claim 1, further including a step ofcleaning the optical film laminate including the polarizing filmcomprising the polyvinyl alcohol type resin having the dichroic materialimpregnated therein in the oriented state with a solution containingiodide salt having temperature lower than the glass transitiontemperature of the non-crystallizable ester type thermoplastic resinsubstrate included in the optical film laminate.
 22. A method formanufacturing an optical film laminate as defined by claim 1, furtherincluding a step of drying the optical film laminate at a temperature of50° C. to 100° C.
 23. A method for manufacturing an optical filmlaminate as defined by claim 1, further including a step of attaching aseparator film through an adhesive agent to a surface of the polarizingfilm opposite to the surface which is attached to the non-crystallizableester type thermoplastic resin substrate included in the optical filmlaminate.
 24. A method for manufacturing an optical film laminate asdefined by claim 1, further including a step of attaching an opticallyfunctional film through a bonding agent to a surface of the polarizingfilm opposite to the surface which is attached to the non-crystallizableester type thermoplastic resin substrate included in the optical filmlaminate.
 25. A method for manufacturing an optical film laminate asdefined by claim 24, further including a step of attaching the separatorfilm through an adhesive agent to the other surface of the opticallyfunctional film.
 26. A method for manufacturing an optical film laminateas defined by claim 1, further including a step of attaching anoptically functional film through a bonding agent to the surface of thepolarizing film opposite to the surface which is attached to thenon-crystallizable ester type resin substrate included in the opticalfilm laminate, and simultaneously peeling the non-crystallizable estertype resin substrate from the polarizing film to transfer the polarizingfilm to the optically functional film for forming an opticallyfunctional film laminate which has the polarizing film transferred tothe optically functional film.
 27. A method for manufacturing an opticalfilm laminate as defined by claim 26, further including a step ofattaching the separator film through an adhesive agent to the surface ofthe polarizing film opposite to the surface which is attached to theoptically functional film.
 28. A method for manufacturing an opticalfilm laminate as defined by claim 26, further including a step ofattaching a second optically functional film through the bonding agentto the surface of the polarizing film opposite to the surface which isattached to the optically functional film, and attaching a separatorfilm through a bonding agent to the second optically functional film.